Solve 9x − 8 = 100

The solution of 9x − 8 = 100 is x = 12.

9x - 8 = 100\ \Rightarrow\ x = 12

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The lines y = 9x − 8 and y = 100 meet at x = 12. The solution of the equation is the x-coordinate of the point where the two sides are equal.

How to work it out

1
The goal is to get x alone. Undo the operations in the opposite order: first the subtraction, then the multiplication.
$9x - 8 = 100$
2
Add 8 to both sides:
$9x - 8 + 8 = 100 + 8 \ \Rightarrow\ 9x = 108$
3
Divide both sides by 9:
$\frac{9x}{9} = \frac{108}{9} \ \Rightarrow\ x = 12$
4
Check: put x = 12 back into the equation.
$9\cdot12 - 8 = 108 - 8 = 100 \checkmark$

LaTeX source of the formulas on this page

\[ 9x - 8 = 100\ \Rightarrow\ x = 12 \]
\[ 9x - 8 = 100 \]
\[ 9x - 8 + 8 = 100 + 8 \ \Rightarrow\ 9x = 108 \]
\[ \frac{9x}{9} = \frac{108}{9} \ \Rightarrow\ x = 12 \]
\[ 9\cdot12 - 8 = 108 - 8 = 100 \checkmark \]

Trying values of x in 9x − 8 = 100

x	9x − 8	Equals 100?
10	82	no
11	91	no
12	100	yes
13	109	no
14	118	no

Questions

What is x in 9x − 8 = 100?

The solution of 9x − 8 = 100 is x = 12.

How do you solve 9x − 8 = 100?

Add 8 to both sides to get 9x = 108, then divide both sides by 9 to get x = 12.

How do I check the answer?

Replace x by 12: 9(12) − 8 = 100, which is 100.

Solve 9x − 8 = 100

How to work it out

Trying values of x in 9x − 8 = 100

Questions

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