Solve 4x − 12 = 40

The solution of 4x − 12 = 40 is x = 13.

4x - 12 = 40\ \Rightarrow\ x = 13

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The lines y = 4x − 12 and y = 40 meet at x = 13. 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.
$4x - 12 = 40$
2
Add 12 to both sides:
$4x - 12 + 12 = 40 + 12 \ \Rightarrow\ 4x = 52$
3
Divide both sides by 4:
$\frac{4x}{4} = \frac{52}{4} \ \Rightarrow\ x = 13$
4
Check: put x = 13 back into the equation.
$4\cdot13 - 12 = 52 - 12 = 40 \checkmark$

LaTeX source of the formulas on this page

\[ 4x - 12 = 40\ \Rightarrow\ x = 13 \]
\[ 4x - 12 = 40 \]
\[ 4x - 12 + 12 = 40 + 12 \ \Rightarrow\ 4x = 52 \]
\[ \frac{4x}{4} = \frac{52}{4} \ \Rightarrow\ x = 13 \]
\[ 4\cdot13 - 12 = 52 - 12 = 40 \checkmark \]

Trying values of x in 4x − 12 = 40

x	4x − 12	Equals 40?
11	32	no
12	36	no
13	40	yes
14	44	no
15	48	no

Questions

What is x in 4x − 12 = 40?

The solution of 4x − 12 = 40 is x = 13.

How do you solve 4x − 12 = 40?

Add 12 to both sides to get 4x = 52, then divide both sides by 4 to get x = 13.

How do I check the answer?

Replace x by 13: 4(13) − 12 = 40, which is 40.

Solve 4x − 12 = 40

How to work it out

Trying values of x in 4x − 12 = 40

Questions

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