Solve 12x + 15 = −81

The solution of 12x + 15 = −81 is x = -8.

12x + 15 = -81\ \Rightarrow\ x = -8

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The lines y = 12x + 15 and y = -81 meet at x = -8. 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.
$12x + 15 = -81$
2
Subtract 15 from both sides:
$12x + 15 - 15 = -81 - 15 \ \Rightarrow\ 12x = -96$
3
Divide both sides by 12:
$\frac{12x}{12} = \frac{-96}{12} \ \Rightarrow\ x = -8$
4
Check: put x = -8 back into the equation.
$12\cdot(-8) + 15 = -96 + 15 = -81 \checkmark$

LaTeX source of the formulas on this page

\[ 12x + 15 = -81\ \Rightarrow\ x = -8 \]
\[ 12x + 15 = -81 \]
\[ 12x + 15 - 15 = -81 - 15 \ \Rightarrow\ 12x = -96 \]
\[ \frac{12x}{12} = \frac{-96}{12} \ \Rightarrow\ x = -8 \]
\[ 12\cdot(-8) + 15 = -96 + 15 = -81 \checkmark \]

Trying values of x in 12x + 15 = −81

x	12x + 15	Equals -81?
-10	-105	no
-9	-93	no
-8	-81	yes
-7	-69	no
-6	-57	no

Questions

What is x in 12x + 15 = −81?

The solution of 12x + 15 = −81 is x = -8.

How do you solve 12x + 15 = −81?

Subtract 15 from both sides to get 12x = -96, then divide both sides by 12 to get x = -8.

How do I check the answer?

Replace x by -8: 12(-8) + 15 = -81, which is -81.

Solve 12x + 15 = −81

How to work it out

Trying values of x in 12x + 15 = −81

Questions

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