Solve 9x − 15 = −87

The solution of 9x − 15 = −87 is x = -8.

9x - 15 = -87\ \Rightarrow\ x = -8

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The lines y = 9x − 15 and y = -87 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 subtraction, then the multiplication.
$9x - 15 = -87$
2
Add 15 to both sides:
$9x - 15 + 15 = -87 + 15 \ \Rightarrow\ 9x = -72$
3
Divide both sides by 9:
$\frac{9x}{9} = \frac{-72}{9} \ \Rightarrow\ x = -8$
4
Check: put x = -8 back into the equation.
$9\cdot(-8) - 15 = -72 - 15 = -87 \checkmark$

LaTeX source of the formulas on this page

\[ 9x - 15 = -87\ \Rightarrow\ x = -8 \]
\[ 9x - 15 = -87 \]
\[ 9x - 15 + 15 = -87 + 15 \ \Rightarrow\ 9x = -72 \]
\[ \frac{9x}{9} = \frac{-72}{9} \ \Rightarrow\ x = -8 \]
\[ 9\cdot(-8) - 15 = -72 - 15 = -87 \checkmark \]

Trying values of x in 9x − 15 = −87

x	9x − 15	Equals -87?
-10	-105	no
-9	-96	no
-8	-87	yes
-7	-78	no
-6	-69	no

Questions

What is x in 9x − 15 = −87?

The solution of 9x − 15 = −87 is x = -8.

How do you solve 9x − 15 = −87?

Add 15 to both sides to get 9x = -72, then divide both sides by 9 to get x = -8.

How do I check the answer?

Replace x by -8: 9(-8) − 15 = -87, which is -87.

Solve 9x − 15 = −87

How to work it out

Trying values of x in 9x − 15 = −87

Questions

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