Solve 3x − 12 = 39

The solution of 3x − 12 = 39 is x = 17.

3x - 12 = 39\ \Rightarrow\ x = 17

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The lines y = 3x − 12 and y = 39 meet at x = 17. 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.
$3x - 12 = 39$
2
Add 12 to both sides:
$3x - 12 + 12 = 39 + 12 \ \Rightarrow\ 3x = 51$
3
Divide both sides by 3:
$\frac{3x}{3} = \frac{51}{3} \ \Rightarrow\ x = 17$
4
Check: put x = 17 back into the equation.
$3\cdot17 - 12 = 51 - 12 = 39 \checkmark$

LaTeX source of the formulas on this page

\[ 3x - 12 = 39\ \Rightarrow\ x = 17 \]
\[ 3x - 12 = 39 \]
\[ 3x - 12 + 12 = 39 + 12 \ \Rightarrow\ 3x = 51 \]
\[ \frac{3x}{3} = \frac{51}{3} \ \Rightarrow\ x = 17 \]
\[ 3\cdot17 - 12 = 51 - 12 = 39 \checkmark \]

Trying values of x in 3x − 12 = 39

x	3x − 12	Equals 39?
15	33	no
16	36	no
17	39	yes
18	42	no
19	45	no

Questions

What is x in 3x − 12 = 39?

The solution of 3x − 12 = 39 is x = 17.

How do you solve 3x − 12 = 39?

Add 12 to both sides to get 3x = 51, then divide both sides by 3 to get x = 17.

How do I check the answer?

Replace x by 17: 3(17) − 12 = 39, which is 39.

Solve 3x − 12 = 39

How to work it out

Trying values of x in 3x − 12 = 39

Questions

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