Solve 9x − 9 = 99

The solution of 9x − 9 = 99 is x = 12.

9x - 9 = 99\ \Rightarrow\ x = 12

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The lines y = 9x − 9 and y = 99 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.
$9x - 9 = 99$
2
Add 9 to both sides:
$9x - 9 + 9 = 99 + 9 \ \Rightarrow\ 9x = 108$
3
Divide both sides by 9:
$\frac{9x}{9} = \frac{108}{9} \ \Rightarrow\ x = 12$
4
Check: put x = 12 back into the equation.
$9\cdot12 - 9 = 108 - 9 = 99 \checkmark$

LaTeX source of the formulas on this page

\[ 9x - 9 = 99\ \Rightarrow\ x = 12 \]
\[ 9x - 9 = 99 \]
\[ 9x - 9 + 9 = 99 + 9 \ \Rightarrow\ 9x = 108 \]
\[ \frac{9x}{9} = \frac{108}{9} \ \Rightarrow\ x = 12 \]
\[ 9\cdot12 - 9 = 108 - 9 = 99 \checkmark \]

Trying values of x in 9x − 9 = 99

x	9x − 9	Equals 99?
10	81	no
11	90	no
12	99	yes
13	108	no
14	117	no

Questions

What is x in 9x − 9 = 99?

The solution of 9x − 9 = 99 is x = 12.

How do you solve 9x − 9 = 99?

Add 9 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) − 9 = 99, which is 99.

Solve 9x − 9 = 99

How to work it out

Trying values of x in 9x − 9 = 99

Questions

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