Solve 12x − 15 = −99

The solution of 12x − 15 = −99 is x = -7.

12x - 15 = -99\ \Rightarrow\ x = -7

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The lines y = 12x − 15 and y = -99 meet at x = -7. 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.
$12x - 15 = -99$
2
Add 15 to both sides:
$12x - 15 + 15 = -99 + 15 \ \Rightarrow\ 12x = -84$
3
Divide both sides by 12:
$\frac{12x}{12} = \frac{-84}{12} \ \Rightarrow\ x = -7$
4
Check: put x = -7 back into the equation.
$12\cdot(-7) - 15 = -84 - 15 = -99 \checkmark$

LaTeX source of the formulas on this page

\[ 12x - 15 = -99\ \Rightarrow\ x = -7 \]
\[ 12x - 15 = -99 \]
\[ 12x - 15 + 15 = -99 + 15 \ \Rightarrow\ 12x = -84 \]
\[ \frac{12x}{12} = \frac{-84}{12} \ \Rightarrow\ x = -7 \]
\[ 12\cdot(-7) - 15 = -84 - 15 = -99 \checkmark \]

Trying values of x in 12x − 15 = −99

x	12x − 15	Equals -99?
-9	-123	no
-8	-111	no
-7	-99	yes
-6	-87	no
-5	-75	no

Questions

What is x in 12x − 15 = −99?

The solution of 12x − 15 = −99 is x = -7.

How do you solve 12x − 15 = −99?

Add 15 to both sides to get 12x = -84, then divide both sides by 12 to get x = -7.

How do I check the answer?

Replace x by -7: 12(-7) − 15 = -99, which is -99.

Solve 12x − 15 = −99

How to work it out

Trying values of x in 12x − 15 = −99

Questions

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