Solve 9x − 12 = 78

The solution of 9x − 12 = 78 is x = 10.

9x - 12 = 78\ \Rightarrow\ x = 10

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The lines y = 9x − 12 and y = 78 meet at x = 10. 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.
$9x - 12 = 78$
2
Add 12 to both sides:
$9x - 12 + 12 = 78 + 12 \ \Rightarrow\ 9x = 90$
3
Divide both sides by 9:
$\frac{9x}{9} = \frac{90}{9} \ \Rightarrow\ x = 10$
4
Check: put x = 10 back into the equation.
$9\cdot10 - 12 = 90 - 12 = 78 \checkmark$

LaTeX source of the formulas on this page

\[ 9x - 12 = 78\ \Rightarrow\ x = 10 \]
\[ 9x - 12 = 78 \]
\[ 9x - 12 + 12 = 78 + 12 \ \Rightarrow\ 9x = 90 \]
\[ \frac{9x}{9} = \frac{90}{9} \ \Rightarrow\ x = 10 \]
\[ 9\cdot10 - 12 = 90 - 12 = 78 \checkmark \]

Trying values of x in 9x − 12 = 78

x	9x − 12	Equals 78?
8	60	no
9	69	no
10	78	yes
11	87	no
12	96	no

Questions

What is x in 9x − 12 = 78?

The solution of 9x − 12 = 78 is x = 10.

How do you solve 9x − 12 = 78?

Add 12 to both sides to get 9x = 90, then divide both sides by 9 to get x = 10.

How do I check the answer?

Replace x by 10: 9(10) − 12 = 78, which is 78.

Solve 9x − 12 = 78

How to work it out

Trying values of x in 9x − 12 = 78

Questions

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