Solve 8x + 15 = −57

The solution of 8x + 15 = −57 is x = -9.

8x + 15 = -57\ \Rightarrow\ x = -9

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The lines y = 8x + 15 and y = -57 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.
$8x + 15 = -57$
2
Subtract 15 from both sides:
$8x + 15 - 15 = -57 - 15 \ \Rightarrow\ 8x = -72$
3
Divide both sides by 8:
$\frac{8x}{8} = \frac{-72}{8} \ \Rightarrow\ x = -9$
4
Check: put x = -9 back into the equation.
$8\cdot(-9) + 15 = -72 + 15 = -57 \checkmark$

LaTeX source of the formulas on this page

\[ 8x + 15 = -57\ \Rightarrow\ x = -9 \]
\[ 8x + 15 = -57 \]
\[ 8x + 15 - 15 = -57 - 15 \ \Rightarrow\ 8x = -72 \]
\[ \frac{8x}{8} = \frac{-72}{8} \ \Rightarrow\ x = -9 \]
\[ 8\cdot(-9) + 15 = -72 + 15 = -57 \checkmark \]

Trying values of x in 8x + 15 = −57

x	8x + 15	Equals -57?
-11	-73	no
-10	-65	no
-9	-57	yes
-8	-49	no
-7	-41	no

Questions

What is x in 8x + 15 = −57?

The solution of 8x + 15 = −57 is x = -9.

How do you solve 8x + 15 = −57?

Subtract 15 from 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 = -57, which is -57.

Solve 8x + 15 = −57

How to work it out

Trying values of x in 8x + 15 = −57

Questions

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