Solve 3x + 9 = −18

The solution of 3x + 9 = −18 is x = -9.

3x + 9 = -18\ \Rightarrow\ x = -9

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The lines y = 3x + 9 and y = -18 meet at x = -9. 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.
$3x + 9 = -18$
2
Subtract 9 from both sides:
$3x + 9 - 9 = -18 - 9 \ \Rightarrow\ 3x = -27$
3
Divide both sides by 3:
$\frac{3x}{3} = \frac{-27}{3} \ \Rightarrow\ x = -9$
4
Check: put x = -9 back into the equation.
$3\cdot(-9) + 9 = -27 + 9 = -18 \checkmark$

LaTeX source of the formulas on this page

\[ 3x + 9 = -18\ \Rightarrow\ x = -9 \]
\[ 3x + 9 = -18 \]
\[ 3x + 9 - 9 = -18 - 9 \ \Rightarrow\ 3x = -27 \]
\[ \frac{3x}{3} = \frac{-27}{3} \ \Rightarrow\ x = -9 \]
\[ 3\cdot(-9) + 9 = -27 + 9 = -18 \checkmark \]

Trying values of x in 3x + 9 = −18

x	3x + 9	Equals -18?
-11	-24	no
-10	-21	no
-9	-18	yes
-8	-15	no
-7	-12	no

Questions

What is x in 3x + 9 = −18?

The solution of 3x + 9 = −18 is x = -9.

How do you solve 3x + 9 = −18?

Subtract 9 from both sides to get 3x = -27, then divide both sides by 3 to get x = -9.

How do I check the answer?

Replace x by -9: 3(-9) + 9 = -18, which is -18.

Solve 3x + 9 = −18

How to work it out

Trying values of x in 3x + 9 = −18

Questions

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