STRAND B: Number Theory. UNIT B2 Number Classification and Bases: Text * * * * * Contents. Section. B2.1 Number Classification. B2.

Transcription

1 STRAND B: Number Theory B2 Number Classification and Bases Text Contents * * * * * Section B2. Number Classification B2.2 Binary Numbers B2.3 Adding and Subtracting Binary Numbers B2.4 Multiplying Binary Numbers B2.5 Other Bases

2 B2 Number Classification and Bases B2. Number Classification The number system is classified into various categories. Natural numbers (or 'counting numbers') These are the positive whole numbers, namely, 2, 3,,,... Integers These are the set of positive and negative whole numbers, e.g., 0, 364, 7, 02. The set of integers is denoted by Z. Rational Numbers A rational number is a number which can be written in the form m, where m and n are integers. n For example, 4 5 is a rational number. A rational number is in its simplest form if m and n have no common factor and n is positive. The set of rational numbers is denoted by Q. Irrational Numbers There are numbers which cannot be written in the form m, where m and n are integers. n Examples of irrational numbers are π, 2, 3, 5. Terminating Decimals These are decimal numbers which stop after a certain number of decimal places. For example, 7 = is a terminating decimal because it stops (terminates) after 3 decimal places. Recurring Decimals These are decimal numbers which keep repeating a digit or group of digits; for example = is a recurring decimal. The six digits repeat in this order. Recurring decimals are written with dots over the first and last digit of the repeating digits, e.g

3 B2. Note All terminating and recurring decimals can be written in the form m, so they are n rational numbers. Real Numbers These are made up of all possible rational and irrational numbers; the set of real numbers is denoted by R. We can use a Venn diagram to illustrate this classification of number, as shown here. R + 2 Q + Q 2π π N Z R : Real numbers N : Natural numbers Z : Integers Q : Rational numbers Q + : Positive rational numbers Some numbers have been inserted to illustrate each set. Worked Example Classify the following numbers as integers, rational, irrational, recurring decimals, terminating decimals. 5, 7, 0.6, , 8,, 0, π 4, 49 2

4 B2. Number Rational Irrational Integer Recurring Terminating Decimal Decimal π 4 49 Worked Example 2 Show that the numbers and are rational. For a terminating decimal the proof is straightforward = = which is rational because m = 69 and n = 200 are integers. For a recurring decimal, we multiply by a power of ten so that after the decimal point we have only the repeating digits = Also = Subtracting the second equation from the first gives = 97 which is rational because m = 97 and n = ( ) = =

5 B2. Worked Example 3 Prove that 3 is irrational. Assume that 3 is rational so we can find integers m and n such that 3 = m n, and m and n have no common factors. Square both sides, 2 3 = m n 2 Multiply both sides by n 2, m 2 2 = 3n Since 3n 2 is divisible by 3, then m 2 is divisible by 3. Since m is an integer, m 2 is an integer and 3 is prime, then m must be divisible by 3. Let m = 3 p, where p is an integer n = m = ( 3p) = 9p 2 2 n = 3p Since 3p 2 is divisible by 3, n 2 is divisible by 3 and hence n is divisible by 3. We have shown that m and n are both divisible by 3. This contradicts the original assumption that 3 = m, where m and n are integers with n no factor common. Our original assumption is wrong. 3 is not rational it is irrational. Exercises. Classify the following numbers as rational or irrational, terminating or recurring decimals. (a) 00 (b) 06. (c) π 02. (d) 3 99 (e) 075. (f) π (g) (h) 6. 4 (i) π 2 (j) 5 (k) sin 45 (l) cos60 4

6 B2. 2. Where possible, write each of the following numbers in the form and n are integers with no common factors (a) 0.49 (b) 03. (c) 49 4 (e) 0.47 (f) 0. (g) 009. (i) 0.25 (j) (d) 7 (h) m n, where m Write each of the following recurring decimals in the form integers with no common factors. m, where m and n are n (a) 04. (b) (c) (d) 08. (e) (f) 05. (g) Given the rational numbers a = 2 3, b = 7 9, c = 5, d = 8 show that a+ b, c+ d, a+ c+ d, ab, cd, bc and abc are rational numbers. 5. Prove that the following numbers are irrational, 2, 5, 6. What happens if you try to prove that 4 is irrational using the proof by a contradiction method. 7. Write down two rational numbers and two irrational numbers which lie in each of the following intervals. (a) 0< x < (b) < x < 9 (c) 4< x < 2 (d) 98 < x < Which of these expressions can be written as recurring decimals and which can be written as non-recurring decimals? 2 7, π, 7, 7, x = a + b State whether x is rational or irrational in each of the following cases, and show sufficient working to justify each answer. (a) a = 5 and b = 2 (b) a = 5 and b = 6 (c) a = 2 and b = 7 (d) a = 3 7 and b = 4 7 5

7 B2. 0. (a) Write down two irrational numbers that multiply together to give a rational number. (b) Which of the following numbers are rational? 2 2, 2 2, 4 2, 4 2, π 2, π 2. (a) A Mathematics student attempted to define an irrational number as follows: "An irrational number is a number which, in its decimal form, goes on and on." (i) Give an example to show that this definition is not correct. (ii) What must be added to the definition to make it correct? (b) Which of the following are rational and which are irrational? 4, 6, , 3 Express each of the rational numbers in the form integers. 3 2 p, where p and q are q 2. (a) Write down an irrational number that lies between 4 and 5. (b) N is a rational number which is not equal to zero. Show clearly why N must also be rational. 3. n is a positive integer such that n = 5. 4 correct to decimal place. (a) (i) Find a value of n. (b) (ii) Explain why n is irrational. Write down a number between 0 and that has a rational square root. B2.2 Binary Numbers We normally work with numbers in base 0. In this section we consider numbers in base 2, often called binary numbers. In base 0 we use the digits 0,, 2, 3, 4, 5, 6, 7, 8, and 9. In base 2 we use only the digits 0 and. Binary numbers are at the heart of all computing systems since, in an electrical circuit, 0 represents no current flowing whereas represents a current flowing. 6

8 B2.2 In base 0 we use a system of place values as shown below: Note that, to obtain the place value for the next digit to the left, we multiply by 0. If we were to add another digit to the front (left) of the numbers above, that number would represent 0 000s. In base 2 we use a system of place values as shown below: = = 73 Note that the place values begin with and are multiplied by 2 as you move to the left. Once you know how the place value system works, you can convert binary numbers to base 0, and vice versa. Worked Example Convert the following binary numbers to base 0: (a) (b) 0 (c) 000 For each number, consider the place value of every digit. (a) = 7 The binary number is 7 in base 0. (b) = 5 The binary number 0 is 5 in base 0. (c) = 02 The binary number 000 is 02 in base 0. 7

9 B2.2 Worked Example 2 Convert the following base 0 numbers into binary numbers: (a) 3 (b) (c) 40 We need to write these numbers in terms of the binary place value headings, 2, 4, 8, 6, 32, 64, 28,..., etc. (a) 2 3 = 2 + The base 0 number 3 is written as in base 2. (b) = The base 0 number is written as 0 in base 2. (c) = The base 0 number 40 is written as in base 2. Exercises. Convert the following binary numbers to base 0: (a) 0 (b) (c) 00 (d) 0 (e) 000 (f) 0 (g) (h) 000 (i) 0000 (j) 000 (k) 000 (l) Convert the following base 0 numbers to binary numbers: (a) 9 (b) 8 (c) 4 (d) 7 (e) 8 (f) 30 (g) 47 (h) 52 (i) 67 (j) 84 (k) 200 (l) Convert the following base 0 numbers to binary numbers: (a) 5 (b) 9 (c) 7 (d) 33 Describe any pattern that you notice in these binary numbers. What will be the next base 0 number that will fit this pattern? 4. Convert the following base 0 numbers to binary numbers: (a) 3 (b) 7 (c) 5 (d) 3 What is the next base 0 number that will continue your binary pattern? 8

10 B A particular binary number has 3 digits. (a) What are the largest and smallest possible binary numbers? (b) Convert these numbers to base When a particular base 0 number is converted it gives a 4-digit binary number. What could the original base 0 number be? 7. A 4-digit binary number has 2 zeros and 2 ones. (a) List all the possible binary numbers with these digits. (b) Convert these numbers to base A binary number has 8 digits and is to be converted to base 0. (a) What is the largest possible base 0 answer? (b) What is the smallest possible base 0 answer? 9. The base 0 number 999 is to be converted to binary. How many more digits does the binary number have than the number in base 0? 0. Calculate the difference between the base 0 number and the binary number, giving your answer in base 0. B2.3 Adding and Subtracting Binary Numbers It is possible to add and subtract binary numbers in a similar way to base 0 numbers. For example, + + = 3 in base 0 becomes + + = in binary. In the same way, 3 = 2 in base 0 becomes = 0 in binary. When you add and subtract binary numbers you will need to be careful when 'carrying' or 'borrowing' as these will take place more often. Key Addition Results for Binary Numbers + 0 = + = = Key Subtraction Results for Binary Numbers 0 = 0 = = 0 9

11 B2.3 Worked Example Calculate, using binary numbers: (a) + 00 (b) (c) + (a) (b) 0 (c) Note how important it is to 'carry' correctly. Worked Example 2 Calculate the binary numbers: (a) 0 (b) 0 (c) 00 0 (a) (b) 0 (c) Exercises. Calculate the binary numbers: (a) + (b) + (c) + (d) + 0 (e) 0 + (f) (g) + 00 (h) (i) (j) (k) 0 + (l) Calculate the binary numbers: (a) 0 (b) 0 0 (c) 0 (d) 00 0 (e) 00 (f) 000 (g) 0 0 (h) 0 0 (i) (j) (k) 0 (l) 0 0

12 B Calculate the binary numbers: (a) + (b) + (c) + (d) + Describe any patterns that you observe in your answers. 4. Calculate the binary numbers: (a) (b) (c) (d) Describe any patterns that you observe in your answers. 5. Solve the following equations, where all numbers, including x, are binary: (a) x + = 0 (b) x 0 = 0 (c) x 0 = 0 (d) x + 0 = 000 (e) x + = 0 (f) x 00 = 0 6. Calculate the binary numbers: (a) 0 (b) 00 (c) 000 (d) 0000 Describe any patterns that you observe in your answers. 7. (a) Convert the binary numbers 0 and 0 to base 0. (b) Add together the two base 0 numbers. (c) Add together the two binary numbers. (d) Convert your answer to base 0 and compare with your answer to (b). 8. (a) Convert the binary numbers 0 and 0 to base 0. (b) Calculate the difference between the two base 0 numbers. (c) Convert your answer to (b) into a binary number. (d) Calculate the difference between the two binary numbers and compare with your answer to (c). 9. Here are 3 binary numbers: Working in binary, (a) add together the two smaller numbers, (b) add together the two larger numbers,

13 B2.3 (c) (d) take the smallest number away from the largest number, add together all three numbers. 0. Calculate the binary numbers: (a) (b) B2.4 Multiplying Binary Numbers Long multiplication can be carried out with binary numbers and is explored in this section. Note that multiplying by numbers like 0, 00 and 000 is very similar to working with base 0 numbers. Worked Example Calculate the binary numbers: (a) 0 00 (b) (c) Check your answers to (a) and (c) by converting each number to base 0. (a) 0 00 = 000 (b) = (c) = Checking: (a) = = 44 and 4 = 44, as expected. (c) =

14 B = 432 and 27 6 = 432, as expected. Note: clearly it is more efficient to keep the numbers in binary when doing the calculations. Worked Example 2 Calculate the binary numbers: (a) 0 (b) 0 0 (c) 0 (d) 0 00 (a) 0 (b) (c) 0 (d) Exercises. Calculate the binary numbers: (a) 0 (b) (c) (d) (e) (f) (g) (h) Check your answers by converting to base 0 numbers. 3

15 B Calculate the binary numbers: (a) (b) 0 (c) 0 0 (d) 0 (e) 0 0 (f) 00 0 (g) 00 0 (h) 00 (i) 00 0 (j) Solve the following equations, where all numbers, including x, are binary: (a) (c) x = 0 (b) x 0 = (d) x = 0 0 x = 0 4. Multiply each of the following binary numbers by itself: (a) (b) (c) What do you notice about your answers to parts (a), (b) and (c)? What will you get if you multiply by itself? 5. Multiply each of the following binary numbers by itself: (a) 0 (b) 00 (c) 000 (d) 0000 What would you expect to get if you multiplied by itself? 6. Calculate the binary numbers: (a) ( ) (b) 0 ( 0) ( ) (d) 0 ( ) (c) Here are 3 binary numbers: Working in binary, (a) multiply the two larger numbers, (b) multiply the two smaller numbers. 8. (a) Multiply the base 0 numbers 45 and 33. (b) Convert your answer to a binary number. (c) Convert 45 and 33 to binary numbers. (d) Multiply the binary numbers obtained in part (c) and compare this answer with your answer to part (b). 4

16 B2.5 Other Bases The ideas that we have considered can be extended to other number bases. The table lists the digits used in some other number bases. Base Digits Used 2 0, 3 0,, 2 4 0,, 2, 3 5 0, 2, 3, 4 The powers of the base number give the place values when you convert to base 0. For example, for base 3, the place values are the powers of 3, i.e., 3, 9, 27, 8, 243, etc. This is shown in the following example, which also shows how the base 3 number 200 is equivalent to the base 0 number 44. Base ( 8) + (2 27) + ( 9) + (0 3) + (0 ) = 44 in base 0 The following example shows a conversion from base 5 to base 0 using the powers of 5 as place values. Base (4 625) + ( 25) + (0 25) + (0 5) + ( ) = 2626 in base 0 Worked Example Convert each of the following numbers to base 0: (a) 42 in base 6. (b) 374 in base 9. (c) 432 in base 5. (a) (4 36) + ( 6) + ( 2 ) = 52 in base 0 (b) (3 8) + (7 9) + (4 ) = 30 in base 0 (c) ( 25) + (4 25) + (3 5) + (2 ) = 242 in base 0 5

17 B2.5 Worked Example 2 Convert each of the following base 0 numbers to the base stated: (a) 472 to base 4, (b) 79 to base 7, (c) 342 to base 3. (a) For base 4 the place values are 256, 64, 6, 4,, and you need to express the number 472 as a linear combination of 256, 64, 6, 4 and, but with no multiplier greater than 3. We begin by writing 472 = ( 256) + 26 The next stage is to write the remaining 26 as a linear combination of 64, 6, 4 and. We use the fact that 26 = (3 64) + 24 and, continuing in this way, 24 = ( 6) = (2 4) + 0 Putting all these stages together, 472 = ( 256) + (3 64) + ( 6) + ( 2 4) + ( 0 ) = 320 in base 4 (b) For base 7 the place values are 49, 7,. 79 = (3 49) + (4 7) + (4 ) = 344 in base 7 (b) For base 3 the place values are 243, 8, 27, 9, 3,. 342 = ( 243) + ( 8) + (0 27) + (2 9) +( 0 3) + (0 ) = 0200 in base 3 Worked Example 3 Carry out each of the following calculations in the base stated: (a) base 5 (b) base 7 (c) base 5 (d) base 3 Check your answer in (a) by changing to base 0 numbers. 6

18 B2.5 (a) Note that 4 + = 0 in base 5. (b) Note that = in base 7. (c) Note that + 4 = 0 in base 5. (d) Note that, in base 3, 2 + = = = Checking in (a): (a) 5 4 ( 5) + (4 ) = (2 5) + ( ) = (4 5) + (0 ) = 20 and 9 + = 20, as expected. Worked Example 4 Carry out each of the following multiplications in the base stated: (a) 4 23 in base 5 (b) 22 2 in base 3 (c) in base 6 Check your answer to (b) by converting to base 0 numbers. 7

19 B2.5 (a) 4 Note that, in base 5, = = (b) 2 2 Note that, in base 3, = (c) 5 2 Note that, in base 6, = = = Checking in (b): (b) ( 9) + (2 3) + (2 ) = ( 3) + (2 ) = ( 8) + (0 27) + (0 9) + (3 ) + ( ) = 85 and 7 5 = 85, as expected. 8

20 B2.5 Exercises. Convert the following numbers from the base stated to base 0: (a) 42 base 5 (b) 333 base 4 (c) 728 base 9 (d) 20 base 3 (e) 47 base 8 (f) 62 base 7 (g) 35 base 6 (h) base 3 2. Convert the following numbers from base 0 to the base stated: (a) 24 to base 3 (b) 6 to base 4 (c) 32 to base 5 (d) 3 to base 6 (e) 34 to base 7 (f) 84 to base 9 (g) 42 to base 3 (h) 67 to base 5 3. Carry out the following additions in the base stated: (a) in base 4 (b) in base 9 (c) in base 8 (d) in base 3 (e) in base 9 (f) in base 6 4. In what number bases could each of the following numbers be written: (a) 23 (b) 2 (c) Carry out each of the following calculations in the base stated: (a) in base 4 (b) in base 5 (c) in base 3 (d) in base 4 (e) in base 7 (f) in base 5 (g) in base 4 (h) in base 5 Check your answers to parts (a), (c) and (e) by converting to base 0 numbers. 6. Carry out each of the following multiplications in the base stated: (a) 3 2 in base 4 (b) 4 3 in base 5 (c) 4 2 in base 6 (d) 3 5 in base 6 (e) 2 2 in base 3 (f) 8 8 in base 9 9

21 B Carry out each of the following multiplications in the base stated: (a) 2 in base 3 (b) 33 2 in base 4 (c) 3 24 in base 5 (d) 42 4 in base 5 (e) 6 24 in base 7 (f) in base 8 (g) in base 5 (h) 20 2 in base 3 Check your answers to parts (a), (c) and (e) by converting to base 0 numbers. 8. In which base was each of the following calculations carried out? (a) = (b) = 3 (c) 8 2 = 7 (d) 4 5 = 32 (e) 3 = 5 (f) 22 4 = 3 9. (a) Change 47 in base 8 into a base 3 number. (b) Change 32 in base 4 into a base 7 number. (c) Change 72 in base 9 into a base 4 number. (d) Change 324 in base 5 into a base 6 number. 0. In which base was each of the following calculations carried out? (a) 7 2 = 2272 (b) 22 2 = 02 (c) = 252 (d) =