Solve 12x − 9 = −21

The solution of 12x − 9 = −21 is x = -1.

12x - 9 = -21\ \Rightarrow\ x = -1

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The lines y = 12x − 9 and y = -21 meet at x = -1. 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.
$12x - 9 = -21$
2
Add 9 to both sides:
$12x - 9 + 9 = -21 + 9 \ \Rightarrow\ 12x = -12$
3
Divide both sides by 12:
$\frac{12x}{12} = \frac{-12}{12} \ \Rightarrow\ x = -1$
4
Check: put x = -1 back into the equation.
$12\cdot(-1) - 9 = -12 - 9 = -21 \checkmark$

LaTeX source of the formulas on this page

\[ 12x - 9 = -21\ \Rightarrow\ x = -1 \]
\[ 12x - 9 = -21 \]
\[ 12x - 9 + 9 = -21 + 9 \ \Rightarrow\ 12x = -12 \]
\[ \frac{12x}{12} = \frac{-12}{12} \ \Rightarrow\ x = -1 \]
\[ 12\cdot(-1) - 9 = -12 - 9 = -21 \checkmark \]

Trying values of x in 12x − 9 = −21

x	12x − 9	Equals -21?
-3	-45	no
-2	-33	no
-1	-21	yes
0	-9	no
1	3	no

Questions

What is x in 12x − 9 = −21?

The solution of 12x − 9 = −21 is x = -1.

How do you solve 12x − 9 = −21?

Add 9 to both sides to get 12x = -12, then divide both sides by 12 to get x = -1.

How do I check the answer?

Replace x by -1: 12(-1) − 9 = -21, which is -21.

Solve 12x − 9 = −21

How to work it out

Trying values of x in 12x − 9 = −21

Questions

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