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 subtraction, then the multiplication.
$8x - 15 = 57$
2
Add 15 to 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.
$8\cdot9 - 15 = 72 - 15 = 57 \checkmark$

LaTeX source of the formulas on this page

\[ 8x - 15 = 57\ \Rightarrow\ x = 9 \]
\[ 8x - 15 = 57 \]
\[ 8x - 15 + 15 = 57 + 15 \ \Rightarrow\ 8x = 72 \]
\[ \frac{8x}{8} = \frac{72}{8} \ \Rightarrow\ x = 9 \]
\[ 8\cdot9 - 15 = 72 - 15 = 57 \checkmark \]

Trying values of x in 8x − 15 = 57

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

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 = 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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