Solve 4x − 8 = 72

The solution of 4x − 8 = 72 is x = 20.

4x - 8 = 72\ \Rightarrow\ x = 20

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The lines y = 4x − 8 and y = 72 meet at x = 20. 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.
$4x - 8 = 72$
2
Add 8 to both sides:
$4x - 8 + 8 = 72 + 8 \ \Rightarrow\ 4x = 80$
3
Divide both sides by 4:
$\frac{4x}{4} = \frac{80}{4} \ \Rightarrow\ x = 20$
4
Check: put x = 20 back into the equation.
$4\cdot20 - 8 = 80 - 8 = 72 \checkmark$

LaTeX source of the formulas on this page

\[ 4x - 8 = 72\ \Rightarrow\ x = 20 \]
\[ 4x - 8 = 72 \]
\[ 4x - 8 + 8 = 72 + 8 \ \Rightarrow\ 4x = 80 \]
\[ \frac{4x}{4} = \frac{80}{4} \ \Rightarrow\ x = 20 \]
\[ 4\cdot20 - 8 = 80 - 8 = 72 \checkmark \]

Trying values of x in 4x − 8 = 72

x	4x − 8	Equals 72?
18	64	no
19	68	no
20	72	yes
21	76	no
22	80	no

Questions

What is x in 4x − 8 = 72?

The solution of 4x − 8 = 72 is x = 20.

How do you solve 4x − 8 = 72?

Add 8 to both sides to get 4x = 80, then divide both sides by 4 to get x = 20.

How do I check the answer?

Replace x by 20: 4(20) − 8 = 72, which is 72.

Solve 4x − 8 = 72

How to work it out

Trying values of x in 4x − 8 = 72

Questions

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