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 addition, then the multiplication.
$9x + 12 = -78$
2
Subtract 12 from 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.
$9\cdot(-10) + 12 = -90 + 12 = -78 \checkmark$

LaTeX source of the formulas on this page

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

Trying values of x in 9x + 12 = −78

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

Subtract 12 from 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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