Environmental Engineering Reference
In-Depth Information
■
Example 8.34
Problem:
2
0 785
.
×××
××
D
16
748
.
22
.
=
0 785
.
90
90
Solution:
2
93 95
6359
.
×
D
22
.
=
2
22
.
×
6359
=
93 95
.
×
D
22
.
×
6359
2
=
D
93
95
148 9
2
.
=
D
2
148 9
12 20
.
=
=
D
.
D
CHECKING THE ANSWER
After obtaining a solution to an equation, always check it. This is an easy process. All
we need to do is substitute the solution for the unknown quantity in the equation. If the
two sides of the equation are identical, the number substituted is the correct answer.
■
Example 8.35
Problem:
Solve and check 4
x
+ 5 - 7 = 2
x
+ 6.
Solution:
4
x
+ 5 - 7 = 2
x
+ 6
4
x
- 2 = 2
x
+ 6
4
x
= 2
x
+ 8
2
x
= 8
x
= 4
Substituting the answer
x
= 4 in the original equation,
4
x
+ 5 - 7 = 2
x
+ 6
(4 × 4) + 5 - 7 = (2 × 4) + 6
16 + 5 - 7 = 8 + 6
14 = 14
Because the statement 14 = 14 is true, the answer
x
= 4 must be correct.
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