Solve 12x − 9 = 231

The solution of 12x − 9 = 231 is x = 20.

12x - 9 = 231\ \Rightarrow\ x = 20

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The lines y = 12x − 9 and y = 231 meet at x = 20. 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.
$12x - 9 = 231$
2
Add 9 to both sides:
$12x - 9 + 9 = 231 + 9 \ \Rightarrow\ 12x = 240$
3
Divide both sides by 12:
$\frac{12x}{12} = \frac{240}{12} \ \Rightarrow\ x = 20$
4
Check: put x = 20 back into the equation.
$12\cdot20 - 9 = 240 - 9 = 231 \checkmark$

LaTeX source of the formulas on this page

\[ 12x - 9 = 231\ \Rightarrow\ x = 20 \]
\[ 12x - 9 = 231 \]
\[ 12x - 9 + 9 = 231 + 9 \ \Rightarrow\ 12x = 240 \]
\[ \frac{12x}{12} = \frac{240}{12} \ \Rightarrow\ x = 20 \]
\[ 12\cdot20 - 9 = 240 - 9 = 231 \checkmark \]

Trying values of x in 12x − 9 = 231

x	12x − 9	Equals 231?
18	207	no
19	219	no
20	231	yes
21	243	no
22	255	no

Questions

What is x in 12x − 9 = 231?

The solution of 12x − 9 = 231 is x = 20.

How do you solve 12x − 9 = 231?

Add 9 to both sides to get 12x = 240, then divide both sides by 12 to get x = 20.

How do I check the answer?

Replace x by 20: 12(20) − 9 = 231, which is 231.

Solve 12x − 9 = 231

How to work it out

Trying values of x in 12x − 9 = 231

Questions

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