Solve 8x − 15 = −87

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

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

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

LaTeX source of the formulas on this page

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

Trying values of x in 8x − 15 = −87

x	8x − 15	Equals -87?
-11	-103	no
-10	-95	no
-9	-87	yes
-8	-79	no
-7	-71	no

Questions

What is x in 8x − 15 = −87?

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

How do you solve 8x − 15 = −87?

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

How do I check the answer?

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

Solve 8x − 15 = −87

How to work it out

Trying values of x in 8x − 15 = −87

Questions

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