Solve 9x − 15 = 57

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

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

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The lines y = 9x − 15 and y = 57 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.
$9x - 15 = 57$
2
Add 15 to both sides:
$9x - 15 + 15 = 57 + 15 \ \Rightarrow\ 9x = 72$
3
Divide both sides by 9:
$\frac{9x}{9} = \frac{72}{9} \ \Rightarrow\ x = 8$
4
Check: put x = 8 back into the equation.
$9\cdot8 - 15 = 72 - 15 = 57 \checkmark$

LaTeX source of the formulas on this page

\[ 9x - 15 = 57\ \Rightarrow\ x = 8 \]
\[ 9x - 15 = 57 \]
\[ 9x - 15 + 15 = 57 + 15 \ \Rightarrow\ 9x = 72 \]
\[ \frac{9x}{9} = \frac{72}{9} \ \Rightarrow\ x = 8 \]
\[ 9\cdot8 - 15 = 72 - 15 = 57 \checkmark \]

Trying values of x in 9x − 15 = 57

x	9x − 15	Equals 57?
6	39	no
7	48	no
8	57	yes
9	66	no
10	75	no

Questions

What is x in 9x − 15 = 57?

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

How do you solve 9x − 15 = 57?

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 = 57, which is 57.

Solve 9x − 15 = 57

How to work it out

Trying values of x in 9x − 15 = 57

Questions

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