Solve 3x − 15 = 12

The solution of 3x − 15 = 12 is x = 9.

3x - 15 = 12\ \Rightarrow\ x = 9

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The lines y = 3x − 15 and y = 12 meet at x = 9. 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.
$3x - 15 = 12$
2
Add 15 to both sides:
$3x - 15 + 15 = 12 + 15 \ \Rightarrow\ 3x = 27$
3
Divide both sides by 3:
$\frac{3x}{3} = \frac{27}{3} \ \Rightarrow\ x = 9$
4
Check: put x = 9 back into the equation.
$3\cdot9 - 15 = 27 - 15 = 12 \checkmark$

LaTeX source of the formulas on this page

\[ 3x - 15 = 12\ \Rightarrow\ x = 9 \]
\[ 3x - 15 = 12 \]
\[ 3x - 15 + 15 = 12 + 15 \ \Rightarrow\ 3x = 27 \]
\[ \frac{3x}{3} = \frac{27}{3} \ \Rightarrow\ x = 9 \]
\[ 3\cdot9 - 15 = 27 - 15 = 12 \checkmark \]

Trying values of x in 3x − 15 = 12

x	3x − 15	Equals 12?
7	6	no
8	9	no
9	12	yes
10	15	no
11	18	no

Questions

What is x in 3x − 15 = 12?

The solution of 3x − 15 = 12 is x = 9.

How do you solve 3x − 15 = 12?

Add 15 to both sides to get 3x = 27, then divide both sides by 3 to get x = 9.

How do I check the answer?

Replace x by 9: 3(9) − 15 = 12, which is 12.

Solve 3x − 15 = 12

How to work it out

Trying values of x in 3x − 15 = 12

Questions

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