Solve 12x − 9 = −81

The solution of 12x − 9 = −81 is x = -6.

12x - 9 = -81\ \Rightarrow\ x = -6

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The lines y = 12x − 9 and y = -81 meet at x = -6. 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.
$12x - 9 = -81$
2
Add 9 to both sides:
$12x - 9 + 9 = -81 + 9 \ \Rightarrow\ 12x = -72$
3
Divide both sides by 12:
$\frac{12x}{12} = \frac{-72}{12} \ \Rightarrow\ x = -6$
4
Check: put x = -6 back into the equation.
$12\cdot(-6) - 9 = -72 - 9 = -81 \checkmark$

LaTeX source of the formulas on this page

\[ 12x - 9 = -81\ \Rightarrow\ x = -6 \]
\[ 12x - 9 = -81 \]
\[ 12x - 9 + 9 = -81 + 9 \ \Rightarrow\ 12x = -72 \]
\[ \frac{12x}{12} = \frac{-72}{12} \ \Rightarrow\ x = -6 \]
\[ 12\cdot(-6) - 9 = -72 - 9 = -81 \checkmark \]

Trying values of x in 12x − 9 = −81

x	12x − 9	Equals -81?
-8	-105	no
-7	-93	no
-6	-81	yes
-5	-69	no
-4	-57	no

Questions

What is x in 12x − 9 = −81?

The solution of 12x − 9 = −81 is x = -6.

How do you solve 12x − 9 = −81?

Add 9 to both sides to get 12x = -72, then divide both sides by 12 to get x = -6.

How do I check the answer?

Replace x by -6: 12(-6) − 9 = -81, which is -81.

Solve 12x − 9 = −81

How to work it out

Trying values of x in 12x − 9 = −81

Questions

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