Solve 12x − 9 = 135

The solution of 12x − 9 = 135 is x = 12.

12x - 9 = 135\ \Rightarrow\ x = 12

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The lines y = 12x − 9 and y = 135 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.
$12x - 9 = 135$
2
Add 9 to both sides:
$12x - 9 + 9 = 135 + 9 \ \Rightarrow\ 12x = 144$
3
Divide both sides by 12:
$\frac{12x}{12} = \frac{144}{12} \ \Rightarrow\ x = 12$
4
Check: put x = 12 back into the equation.
$12\cdot12 - 9 = 144 - 9 = 135 \checkmark$

LaTeX source of the formulas on this page

\[ 12x - 9 = 135\ \Rightarrow\ x = 12 \]
\[ 12x - 9 = 135 \]
\[ 12x - 9 + 9 = 135 + 9 \ \Rightarrow\ 12x = 144 \]
\[ \frac{12x}{12} = \frac{144}{12} \ \Rightarrow\ x = 12 \]
\[ 12\cdot12 - 9 = 144 - 9 = 135 \checkmark \]

Trying values of x in 12x − 9 = 135

x	12x − 9	Equals 135?
10	111	no
11	123	no
12	135	yes
13	147	no
14	159	no

Questions

What is x in 12x − 9 = 135?

The solution of 12x − 9 = 135 is x = 12.

How do you solve 12x − 9 = 135?

Add 9 to both sides to get 12x = 144, then divide both sides by 12 to get x = 12.

How do I check the answer?

Replace x by 12: 12(12) − 9 = 135, which is 135.

Solve 12x − 9 = 135

How to work it out

Trying values of x in 12x − 9 = 135

Questions

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