Solve 3x + 15 = −9

The solution of 3x + 15 = −9 is x = -8.

3x + 15 = -9\ \Rightarrow\ x = -8

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The lines y = 3x + 15 and y = -9 meet at x = -8. 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.
$3x + 15 = -9$
2
Subtract 15 from both sides:
$3x + 15 - 15 = -9 - 15 \ \Rightarrow\ 3x = -24$
3
Divide both sides by 3:
$\frac{3x}{3} = \frac{-24}{3} \ \Rightarrow\ x = -8$
4
Check: put x = -8 back into the equation.
$3\cdot(-8) + 15 = -24 + 15 = -9 \checkmark$

LaTeX source of the formulas on this page

\[ 3x + 15 = -9\ \Rightarrow\ x = -8 \]
\[ 3x + 15 = -9 \]
\[ 3x + 15 - 15 = -9 - 15 \ \Rightarrow\ 3x = -24 \]
\[ \frac{3x}{3} = \frac{-24}{3} \ \Rightarrow\ x = -8 \]
\[ 3\cdot(-8) + 15 = -24 + 15 = -9 \checkmark \]

Trying values of x in 3x + 15 = −9

x	3x + 15	Equals -9?
-10	-15	no
-9	-12	no
-8	-9	yes
-7	-6	no
-6	-3	no

Questions

What is x in 3x + 15 = −9?

The solution of 3x + 15 = −9 is x = -8.

How do you solve 3x + 15 = −9?

Subtract 15 from both sides to get 3x = -24, then divide both sides by 3 to get x = -8.

How do I check the answer?

Replace x by -8: 3(-8) + 15 = -9, which is -9.

Solve 3x + 15 = −9

How to work it out

Trying values of x in 3x + 15 = −9

Questions

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