Solve 3x + 9 = −12

The solution of 3x + 9 = −12 is x = -7.

3x + 9 = -12\ \Rightarrow\ x = -7

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The lines y = 3x + 9 and y = -12 meet at x = -7. 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 addition, then the multiplication.
$3x + 9 = -12$
2
Subtract 9 from both sides:
$3x + 9 - 9 = -12 - 9 \ \Rightarrow\ 3x = -21$
3
Divide both sides by 3:
$\frac{3x}{3} = \frac{-21}{3} \ \Rightarrow\ x = -7$
4
Check: put x = -7 back into the equation.
$3\cdot(-7) + 9 = -21 + 9 = -12 \checkmark$

LaTeX source of the formulas on this page

\[ 3x + 9 = -12\ \Rightarrow\ x = -7 \]
\[ 3x + 9 = -12 \]
\[ 3x + 9 - 9 = -12 - 9 \ \Rightarrow\ 3x = -21 \]
\[ \frac{3x}{3} = \frac{-21}{3} \ \Rightarrow\ x = -7 \]
\[ 3\cdot(-7) + 9 = -21 + 9 = -12 \checkmark \]

Trying values of x in 3x + 9 = −12

x	3x + 9	Equals -12?
-9	-18	no
-8	-15	no
-7	-12	yes
-6	-9	no
-5	-6	no

Questions

What is x in 3x + 9 = −12?

The solution of 3x + 9 = −12 is x = -7.

How do you solve 3x + 9 = −12?

Subtract 9 from both sides to get 3x = -21, then divide both sides by 3 to get x = -7.

How do I check the answer?

Replace x by -7: 3(-7) + 9 = -12, which is -12.

Solve 3x + 9 = −12

How to work it out

Trying values of x in 3x + 9 = −12

Questions

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