Solve 12x + 8 = −40

The solution of 12x + 8 = −40 is x = -4.

12x + 8 = -40\ \Rightarrow\ x = -4

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The lines y = 12x + 8 and y = -40 meet at x = -4. 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.
$12x + 8 = -40$
2
Subtract 8 from both sides:
$12x + 8 - 8 = -40 - 8 \ \Rightarrow\ 12x = -48$
3
Divide both sides by 12:
$\frac{12x}{12} = \frac{-48}{12} \ \Rightarrow\ x = -4$
4
Check: put x = -4 back into the equation.
$12\cdot(-4) + 8 = -48 + 8 = -40 \checkmark$

LaTeX source of the formulas on this page

\[ 12x + 8 = -40\ \Rightarrow\ x = -4 \]
\[ 12x + 8 = -40 \]
\[ 12x + 8 - 8 = -40 - 8 \ \Rightarrow\ 12x = -48 \]
\[ \frac{12x}{12} = \frac{-48}{12} \ \Rightarrow\ x = -4 \]
\[ 12\cdot(-4) + 8 = -48 + 8 = -40 \checkmark \]

Trying values of x in 12x + 8 = −40

x	12x + 8	Equals -40?
-6	-64	no
-5	-52	no
-4	-40	yes
-3	-28	no
-2	-16	no

Questions

What is x in 12x + 8 = −40?

The solution of 12x + 8 = −40 is x = -4.

How do you solve 12x + 8 = −40?

Subtract 8 from both sides to get 12x = -48, then divide both sides by 12 to get x = -4.

How do I check the answer?

Replace x by -4: 12(-4) + 8 = -40, which is -40.

Solve 12x + 8 = −40

How to work it out

Trying values of x in 12x + 8 = −40

Questions

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