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Coefficient

The coefficient of a quantity records how many of that quantity there are.

Since constants alone do not record the number of some quantity, they are not usually considered as numerical coefficients. For example, in the expression 7 x + 2 y 8 z + 12 size 12{7x+2y - 8z+"12"} {} , the coefficient of

7 x size 12{7x} {} is 7. (There are 7 x 's.)
2 y size 12{2y} {} is 2. (There are 2 y 's.)
8 z size 12{ - 8z} {} is 8 size 12{ - 8} {} . (There are 8 size 12{ - 8} {} z 's.)

The constant 12 is not considered a numerical coefficient.

1 x = x

When the numerical coefficient of a variable is 1, we write only the variable and not the coefficient. For example, we write x size 12{x} {} rather than 1 x size 12{1x} {} . It is clear just by looking at x size 12{x} {} that there is only one.

Numerical evaluation

We know that a variable represents an unknown quantity. Therefore, any expres­sion that contains a variable represents an unknown quantity. For example, if the value of x size 12{x} {} is unknown, then the value of 3 x + 5 size 12{3x+5} {} is unknown. The value of 3 x + 5 size 12{3x+5} {} depends on the value of x size 12{x} {} .

Numerical evaluation

Numerical evaluation is the process of determining the numerical value of an algebraic expression by replacing the variables in the expression with specified numbers.

Sample set b

Find the value of each expression.

2 x + 7 y size 12{2x+7y} {} , if x = - 4 and y = 2 size 12{y=2} {}

Replace x with –4 and y with 2.

2 x + 7 y = 2 ( - 4 ) + 7 ( 2 ) = - 8 + 14 = 6

Thus, when x = 4 and y = 2 , 2 x + 7 y = 6 size 12{2x+7y=6} {} .

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5 a b + 8 b 12 , if a = 6 and b = - 3 .

Replace a with 6 and b with –3.

5 a b + 8 b 12 = 5 ( 6 ) - 3 + 8 ( - 3 ) 12 = 30 - 3 + - 24 12 = - 10 + ( - 2 ) = - 12

Thus, when a = 6 and b = –3, 5a b + 8b 12 = - 12 size 12{ { {5a} over {b} } + { {8b} over {"12"} } "=-""12"} {} .

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6 2 a 15 b size 12{6 left (2a-"15"b right )} {} , if a = - 5 size 12{a"=-"5} {} and b = - 1 size 12{b"=-"1} {}

Replace a with –5 and b with –1.

6 ( 2 a - 15 b ) = 6 ( 2 ( - 5 ) - 15 ( - 1 ) ) = 6 ( - 10 + 15 ) = 6 ( 5 ) = 30

Thus, when a = –5 and b = –1 , 6 2 a 15 b = 30 size 12{6 left (2a-"15"b right )="30"} {} .

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3 x 2 2 x + 1 size 12{3x rSup { size 8{2} } -2x+1} {} , if x = 4 size 12{x=4} {}

Replace x with 4.

3 x 2 - 2 x + 1 = 3 ( 4 ) 2 - 2 ( 4 ) + 1 = 3 16 - 2 ( 4 ) + 1 = 48 - 8 + 1 = 41

Thus, when x = 4 , 3 x 2 2 x + 1 = 41 size 12{3x rSup { size 8{2} } -2x+1="41"} {} .

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x 2 4 size 12{-x rSup { size 8{2} } -4} {} , if x = 3 size 12{x=3} {}

Replace x with 3.

- x 2 - 4 = - 3 2 - 4 Be careful to square only the 3. The exponent 2 is connected   only   to 3, not -3 = - 9 - 4 = - 13

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x 2 4 size 12{ left (-x right ) rSup { size 8{2} } -4} {} , if x = 3 size 12{x=3} {} .

Replace x with 3.

( - x ) 2 - 4 = ( - 3 ) 2 - 4 The exponent is connected to -3, not 3 as in problem 5 above. = 9 - 4 = - 5

The exponent is connected to –3, not 3 as in the problem above.

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Practice set b

Find the value of each expression.

9 m 2 n , size 12{9m-2n,} {} if m = - 2 size 12{m"=-"2} {} and n = 5 size 12{n=5} {}

-28

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3 x 5 y + 2 z size 12{-3x-5y+2z} {} , if x = - 4 size 12{x"=-"4} {} , y = 3 size 12{y=3} {} , z = 0 size 12{z=0} {}

-3

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10 a 3b + 4b 2 size 12{ { {"10"a} over {3b} } + { {4b} over {2} } } {} , if a = - 6 size 12{a"=-"6} {} , and b = 2 size 12{b=2} {}

-6

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8 3 m 5 n size 12{8 left (3m-5n right )} {} , if m = - 4 size 12{m"=-"4} {} and n = - 5 size 12{n"=-"5} {}

104

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3 40 2 4 a 3 b size 12{3 left [-"40"-2 left (4a-3b right ) right ]} {} , if a = - 6 size 12{a"=-"6} {} and b = 0 size 12{b=0} {}

24

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5 y 2 + 6 y 11 size 12{5y rSup { size 8{2} } +6y-"11"} {} , if y = - 1 size 12{y"=-"1} {}

-12

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x 2 + 2 x + 7 size 12{-x rSup { size 8{2} } +2x+7} {} , if x = 4 size 12{x=4} {}

-1

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x 2 + 2 x + 7 size 12{ left (-x right ) rSup { size 8{2} } +2x+7} {} , if x = 4 size 12{x=4} {}

31

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Exercises

In an algebraic expression, terms are separated by signs and factors are separated by signs.

Addition; multiplication

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For the following 8 problems, specify each term.

3 m + 7 n size 12{3m+7n} {}

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5 x + 18 y size 12{5x+"18"y} {}

5 x , 18 y size 12{5x, 18y} {}

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4 a 6 b + c size 12{4a-6b+c} {}

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8 s + 2 r 7 t size 12{8s+2r-7t} {}

8 s , 2 r , 7 t size 12{8s,2r,-7t} {}

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m 3 n 4 a + 7 b size 12{m-3n-4a+7b} {}

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7 a 2 b 3 c 4 d size 12{7a-2b-3c-4d} {}

7 a , 2 b , 3 c , 4 d size 12{7a, -2b, -3c, -4d} {}

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6 a 5 b size 12{-6a-5b} {}

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x y size 12{-x-y} {}

x , y size 12{-x,-y} {}

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What is the function of a numerical coefficient?

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Write 1 m in a simpler way.

m

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Write 1 s in a simpler way.

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In the expression 5 a , how many a ’s are indicated?

5

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In the expression –7 c , how many c ’s are indicated?

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Find the value of each expression.

2 m 6 n size 12{2m-6n} {} , if m = - 3 size 12{m"=-"3} {} and n = 4 size 12{n=4} {}

-30

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5 a + 6 b size 12{5a+6b} {} , if a = - 6 size 12{a"=-"6} {} and b = 5 size 12{b=5} {}

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2 x 3 y + 4 z size 12{2x-3y+4z} {} , if x = 1 size 12{x=1} {} , y = - 1 size 12{y"=-"1} {} , and z = - 2 size 12{z"=-"2} {}

-3

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9 a + 6 b 8 x + 4 y size 12{9a+6b-8x+4y} {} , if a = - 2 size 12{a"=-"2} {} , b = - 1 size 12{b"=-"1} {} , x = - 2 size 12{x"=-"2} {} , and y = 0 size 12{y=0} {}

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8 x 3 y + 18 y 2 x , size 12{ { {8x} over {3y} } + { {"18"y} over {2x} } ,} {} if x = 9 size 12{x=9} {} and y = - 2 size 12{y"=-"2} {}

-14

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3 m 2 n 6 n m , size 12{ { {-3m} over {2n} } - { {-6n} over {m} } ,} {} if m = - 6 size 12{m"=-"6} {} and n = 3 size 12{n=3} {}

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4 3 r + 2 s size 12{4 left (3r+2s right )} {} , if r = 4 size 12{r=4} {} and s = 1 size 12{s=1} {}

56

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3 9 a 6 b size 12{3 left (9a-6b right )} {} , if a = - 1 size 12{a"=-"1} {} and b = - 2 size 12{b"=-"2} {}

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8 5 m + 8 n size 12{-8 left (5m+8n right )} {} , if m = 0 size 12{m=0} {} and n = - 1 size 12{n"=-"1} {}

64

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2 6 x + y 2 z size 12{-2 left (-6x+y-2z right )} {} , if x = 1 size 12{x=1} {} , y = 1 size 12{y=1} {} , and z = 2 size 12{z=2} {}

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10 x 2 y + 5 z size 12{- left ("10"x-2y+5z right )} {} if x = 2 size 12{x=2} {} , y = 8 size 12{y=8} {} , and z = - 1 size 12{z"=-"1} {}

1

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a 3 b + 2 c d size 12{- left (a-3b+2c-d right )} {} , if a = - 5 size 12{a"=-"5} {} , b = 2 size 12{b=2} {} , c = 0 size 12{c=0} {} , and d = - 1 size 12{d"=-"1} {}

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3 16 3 a + 3 b size 12{3 left ["16"-3 left (a+3b right ) right ]} {} , if a = 3 size 12{a=3} {} and b = - 2 size 12{b"=-"2} {}

75

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2 5 a + 2 b b 6 size 12{-2 left [5a+2b left (b-6 right ) right ]} {} , if a = - 2 size 12{a"=-"2} {} and b = 3 size 12{b=3} {}

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6 x + 3 y 2 x + 4 y size 12{- left lbrace 6x+3y left [-2 left (x+4y right ) right ] right rbrace } {} , if x = 0 size 12{x=0} {} and y = 1 size 12{y=1} {}

24

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2 19 6 4 2 a b 7 size 12{-2 left lbrace "19"-6 left [4-2 left (a-b-7 right ) right ] right rbrace } {} , if a = 10 size 12{a="10"} {} and b = 3 size 12{b=3} {}

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x 2 + 3 x 1 size 12{x rSup { size 8{2} } +3x-1} {} , if x = 5 size 12{x=5} {}

39

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m 2 2 m + 6 size 12{m rSup { size 8{2} } -2m+6} {} , if m = 3 size 12{m=3} {}

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6 a 2 + 2 a 15 size 12{6a rSup { size 8{2} } +2a-"15"} {} , if a = - 2 size 12{a"=-"2} {}

5

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5 s 2 + 6 s + 10 , size 12{5s rSup { size 8{2} } +6s+"10",} {} if x = - 1 size 12{x"=-"1} {}

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16 x 2 + 8 x 7 size 12{"16"x rSup { size 8{2} } +8x-7} {} , if x = 0 size 12{x=0} {}

-7

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8 y 2 + 6 y + 11 , size 12{-8y rSup { size 8{2} } +6y+"11",} {} if y = 0 size 12{y=0} {}

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y 6 2 + 3 y 5 + 4 size 12{ left (y-6 right ) rSup { size 8{2} } +3 left (y-5 right )+4} {} , if y = 5 size 12{y=5} {}

5

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x + 8 2 + 4 x + 9 + 1, size 12{ left (x+8 right ) rSup { size 8{2} } +4 left (x+9 right )+1,} {} if x = - 6 size 12{x"=-"6} {}

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Exercises for review

( [link] ) Perform the addition: 5 3 8 + 2 1 6 size 12{5 { {3} over {8} } +2 { {1} over {6} } } {} .

181 24 = 7 13 24 size 12{ { {"181"} over {"24"} } =7 { {"13"} over {"24"} } } {}

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( [link] ) Arrange the numbers in order from smallest to largest: 11 32 , 15 48 , and 7 16 size 12{ { {"11"} over {"32"} } , { {"15"} over {"48"} } ", and " { {7} over {"16"} } } {}

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( [link] ) Find the value of 2 3 2 + 8 27 size 12{ left ( { {2} over {3} } right ) rSup { size 8{2} } + { {8} over {"27"} } } {}

20 27 size 12{ { {"20"} over {"27"} } } {}

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( [link] ) Write the proportion in fractional form: “9 is to 8 as x is to 7.”

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( [link] ) Find the value of 3 2 6 12 size 12{-3 left (2-6 right )-"12"} {}

0

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Source:  OpenStax, Fundamentals of mathematics. OpenStax CNX. Aug 18, 2010 Download for free at http://cnx.org/content/col10615/1.4
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