Solve 12x − 15 = −123

The solution of 12x − 15 = −123 is x = -9.

12x - 15 = -123\ \Rightarrow\ x = -9

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The lines y = 12x − 15 and y = -123 meet at x = -9. 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.
$12x - 15 = -123$
2
Add 15 to both sides:
$12x - 15 + 15 = -123 + 15 \ \Rightarrow\ 12x = -108$
3
Divide both sides by 12:
$\frac{12x}{12} = \frac{-108}{12} \ \Rightarrow\ x = -9$
4
Check: put x = -9 back into the equation.
$12\cdot(-9) - 15 = -108 - 15 = -123 \checkmark$

LaTeX source of the formulas on this page

\[ 12x - 15 = -123\ \Rightarrow\ x = -9 \]
\[ 12x - 15 = -123 \]
\[ 12x - 15 + 15 = -123 + 15 \ \Rightarrow\ 12x = -108 \]
\[ \frac{12x}{12} = \frac{-108}{12} \ \Rightarrow\ x = -9 \]
\[ 12\cdot(-9) - 15 = -108 - 15 = -123 \checkmark \]

Trying values of x in 12x − 15 = −123

x	12x − 15	Equals -123?
-11	-147	no
-10	-135	no
-9	-123	yes
-8	-111	no
-7	-99	no

Questions

What is x in 12x − 15 = −123?

The solution of 12x − 15 = −123 is x = -9.

How do you solve 12x − 15 = −123?

Add 15 to both sides to get 12x = -108, then divide both sides by 12 to get x = -9.

How do I check the answer?

Replace x by -9: 12(-9) − 15 = -123, which is -123.

Solve 12x − 15 = −123

How to work it out

Trying values of x in 12x − 15 = −123

Questions

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