Solve 12x − 9 = 171

The solution of 12x − 9 = 171 is x = 15.

12x - 9 = 171\ \Rightarrow\ x = 15

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The lines y = 12x − 9 and y = 171 meet at x = 15. 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.
$12x - 9 = 171$
2
Add 9 to both sides:
$12x - 9 + 9 = 171 + 9 \ \Rightarrow\ 12x = 180$
3
Divide both sides by 12:
$\frac{12x}{12} = \frac{180}{12} \ \Rightarrow\ x = 15$
4
Check: put x = 15 back into the equation.
$12\cdot15 - 9 = 180 - 9 = 171 \checkmark$

LaTeX source of the formulas on this page

\[ 12x - 9 = 171\ \Rightarrow\ x = 15 \]
\[ 12x - 9 = 171 \]
\[ 12x - 9 + 9 = 171 + 9 \ \Rightarrow\ 12x = 180 \]
\[ \frac{12x}{12} = \frac{180}{12} \ \Rightarrow\ x = 15 \]
\[ 12\cdot15 - 9 = 180 - 9 = 171 \checkmark \]

Trying values of x in 12x − 9 = 171

x	12x − 9	Equals 171?
13	147	no
14	159	no
15	171	yes
16	183	no
17	195	no

Questions

What is x in 12x − 9 = 171?

The solution of 12x − 9 = 171 is x = 15.

How do you solve 12x − 9 = 171?

Add 9 to both sides to get 12x = 180, then divide both sides by 12 to get x = 15.

How do I check the answer?

Replace x by 15: 12(15) − 9 = 171, which is 171.

Solve 12x − 9 = 171

How to work it out

Trying values of x in 12x − 9 = 171

Questions

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