Solve 3x − 12 = −42

The solution of 3x − 12 = −42 is x = -10.

3x - 12 = -42\ \Rightarrow\ x = -10

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The lines y = 3x − 12 and y = -42 meet at x = -10. 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.
$3x - 12 = -42$
2
Add 12 to both sides:
$3x - 12 + 12 = -42 + 12 \ \Rightarrow\ 3x = -30$
3
Divide both sides by 3:
$\frac{3x}{3} = \frac{-30}{3} \ \Rightarrow\ x = -10$
4
Check: put x = -10 back into the equation.
$3\cdot(-10) - 12 = -30 - 12 = -42 \checkmark$

LaTeX source of the formulas on this page

\[ 3x - 12 = -42\ \Rightarrow\ x = -10 \]
\[ 3x - 12 = -42 \]
\[ 3x - 12 + 12 = -42 + 12 \ \Rightarrow\ 3x = -30 \]
\[ \frac{3x}{3} = \frac{-30}{3} \ \Rightarrow\ x = -10 \]
\[ 3\cdot(-10) - 12 = -30 - 12 = -42 \checkmark \]

Trying values of x in 3x − 12 = −42

x	3x − 12	Equals -42?
-12	-48	no
-11	-45	no
-10	-42	yes
-9	-39	no
-8	-36	no

Questions

What is x in 3x − 12 = −42?

The solution of 3x − 12 = −42 is x = -10.

How do you solve 3x − 12 = −42?

Add 12 to both sides to get 3x = -30, then divide both sides by 3 to get x = -10.

How do I check the answer?

Replace x by -10: 3(-10) − 12 = -42, which is -42.

Solve 3x − 12 = −42

How to work it out

Trying values of x in 3x − 12 = −42

Questions

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