Solve 3x − 12 = −9

The solution of 3x − 12 = −9 is x = 1.

3x - 12 = -9\ \Rightarrow\ x = 1

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The lines y = 3x − 12 and y = -9 meet at x = 1. 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.
$3x - 12 = -9$
2
Add 12 to both sides:
$3x - 12 + 12 = -9 + 12 \ \Rightarrow\ 3x = 3$
3
Divide both sides by 3:
$\frac{3x}{3} = \frac{3}{3} \ \Rightarrow\ x = 1$
4
Check: put x = 1 back into the equation.
$3\cdot1 - 12 = 3 - 12 = -9 \checkmark$

LaTeX source of the formulas on this page

\[ 3x - 12 = -9\ \Rightarrow\ x = 1 \]
\[ 3x - 12 = -9 \]
\[ 3x - 12 + 12 = -9 + 12 \ \Rightarrow\ 3x = 3 \]
\[ \frac{3x}{3} = \frac{3}{3} \ \Rightarrow\ x = 1 \]
\[ 3\cdot1 - 12 = 3 - 12 = -9 \checkmark \]

Trying values of x in 3x − 12 = −9

x	3x − 12	Equals -9?
-1	-15	no
0	-12	no
1	-9	yes
2	-6	no
3	-3	no

Questions

What is x in 3x − 12 = −9?

The solution of 3x − 12 = −9 is x = 1.

How do you solve 3x − 12 = −9?

Add 12 to both sides to get 3x = 3, then divide both sides by 3 to get x = 1.

How do I check the answer?

Replace x by 1: 3(1) − 12 = -9, which is -9.

Solve 3x − 12 = −9

How to work it out

Trying values of x in 3x − 12 = −9

Questions

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