Solve 9x − 8 = 172

The solution of 9x − 8 = 172 is x = 20.

9x - 8 = 172\ \Rightarrow\ x = 20

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The lines y = 9x − 8 and y = 172 meet at x = 20. 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.
$9x - 8 = 172$
2
Add 8 to both sides:
$9x - 8 + 8 = 172 + 8 \ \Rightarrow\ 9x = 180$
3
Divide both sides by 9:
$\frac{9x}{9} = \frac{180}{9} \ \Rightarrow\ x = 20$
4
Check: put x = 20 back into the equation.
$9\cdot20 - 8 = 180 - 8 = 172 \checkmark$

LaTeX source of the formulas on this page

\[ 9x - 8 = 172\ \Rightarrow\ x = 20 \]
\[ 9x - 8 = 172 \]
\[ 9x - 8 + 8 = 172 + 8 \ \Rightarrow\ 9x = 180 \]
\[ \frac{9x}{9} = \frac{180}{9} \ \Rightarrow\ x = 20 \]
\[ 9\cdot20 - 8 = 180 - 8 = 172 \checkmark \]

Trying values of x in 9x − 8 = 172

x	9x − 8	Equals 172?
18	154	no
19	163	no
20	172	yes
21	181	no
22	190	no

Questions

What is x in 9x − 8 = 172?

The solution of 9x − 8 = 172 is x = 20.

How do you solve 9x − 8 = 172?

Add 8 to both sides to get 9x = 180, then divide both sides by 9 to get x = 20.

How do I check the answer?

Replace x by 20: 9(20) − 8 = 172, which is 172.

Solve 9x − 8 = 172

How to work it out

Trying values of x in 9x − 8 = 172

Questions

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