Solve 4x − 4 = 72

The solution of 4x − 4 = 72 is x = 19.

4x - 4 = 72\ \Rightarrow\ x = 19

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The lines y = 4x − 4 and y = 72 meet at x = 19. 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.
$4x - 4 = 72$
2
Add 4 to both sides:
$4x - 4 + 4 = 72 + 4 \ \Rightarrow\ 4x = 76$
3
Divide both sides by 4:
$\frac{4x}{4} = \frac{76}{4} \ \Rightarrow\ x = 19$
4
Check: put x = 19 back into the equation.
$4\cdot19 - 4 = 76 - 4 = 72 \checkmark$

LaTeX source of the formulas on this page

\[ 4x - 4 = 72\ \Rightarrow\ x = 19 \]
\[ 4x - 4 = 72 \]
\[ 4x - 4 + 4 = 72 + 4 \ \Rightarrow\ 4x = 76 \]
\[ \frac{4x}{4} = \frac{76}{4} \ \Rightarrow\ x = 19 \]
\[ 4\cdot19 - 4 = 76 - 4 = 72 \checkmark \]

Trying values of x in 4x − 4 = 72

x	4x − 4	Equals 72?
17	64	no
18	68	no
19	72	yes
20	76	no
21	80	no

Questions

What is x in 4x − 4 = 72?

The solution of 4x − 4 = 72 is x = 19.

How do you solve 4x − 4 = 72?

Add 4 to both sides to get 4x = 76, then divide both sides by 4 to get x = 19.

How do I check the answer?

Replace x by 19: 4(19) − 4 = 72, which is 72.

Solve 4x − 4 = 72

How to work it out

Trying values of x in 4x − 4 = 72

Questions

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