Recall that an algebraic expression contains one or more variables. We can substitute a number for each variable and then find the value of the expression.
This process is called evaluating the expression.
For example, to evaluate 2m for m = 5, we would plug 5 for m.
2m = 2(5) = 10
Parentheses are another way to show multiplication.
2(5) = 2 × 5 = 10
Example 1 :
Evaluate the expression for the given value of the variable.
x - 9; x = 15
Solution :
15 - 9 = 6
Therefore, when x = 15, x - 9 = 6.
Example 2 :
Evaluate the expression for the given value of the variable.
16/n; n = 8
Solution :
16/8 = 2
Therefore, when n = 8, 16/n = 2.
Example 3 :
Evaluate the given expression for x = 3 and y = 5.
3x + 2y
Solution :
Substitute x = 3 and y = 5 in the given expression
= 3(3) + 2(5)
= 9 + 10
= 19
Therefore, 3x + 2y = 19.
Example 4 :
Evaluate the given expression for y = 1.4.
0.5y
Solution :
Substitute y = 1.4 in the given expression
= 0.5(1.4)
= 0.5 x 1.4
= 0.7
Therefore, 0.5y = 0.7.
Example 5 :
Evaluate the given expression for s = 5.
s2 + 7s - 2
Solution :
Substitute s = 5 in the given expression
= 52 + 7(5) - 2
= 25 + 35 - 2
= 58
Therefore, s² + 7s - 2 = 58.
Example 6 :
Evaluate the given expression for m = 1/3.
18m2 + 3m + 7
Solution :
Substitute m = 1/3 in the given expression
= 18(1/3)2 + 3(1/3) + 7
= 2 + 1 + 7
= 10
Therefore, 18m² + 3m + 7 = 10.
Example 7 :
Evaluate the given expression for m = 13.
m2 + m - 54
Solution :
Substitute m = 13 in the given expression.
= 132 + 13 -54
= 169 + 13 - 54
= 128
Therefore, m2 + m - 54 = 128.
Example 8 :
Evaluate the given expression for x = 3 and y = 5.
x2 + y2
Solution :
Substitute x = 3 and y = 5 in the given expression.
= 32 + 52
= 9 + 25
= 34
Therefore, x2 + y2 = 34.
Example 9 :
Evaluate the given expression for m = 5 and n = 2.
5m2 + 2m2n
Solution :
Substitute m = 5 and n = 2 in the given expression.
= 5(5)2 + 2(5)2(2)
= 125 + 100
= 225
Therefore, 5m2 + 2m2n = 225.
Example 10 :
Evaluate the given expression for m = 3.
(2m2 + 5m - 7)/2
Solution :
Substitute m = 3 in the given expression
= [2(3)2 + 5(3) - 7]/2
= [18 + 15 - 7]/2
= 26/2
= 13
Therefore, (2m2 + 5m - 7)/2 = 13.
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