Solve 5x − 12 = 78

The solution of 5x − 12 = 78 is x = 18.

5x - 12 = 78\ \Rightarrow\ x = 18

Explain it step by step in chat Make a short video of it

The lines y = 5x − 12 and y = 78 meet at x = 18. 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.
$5x - 12 = 78$
2
Add 12 to both sides:
$5x - 12 + 12 = 78 + 12 \ \Rightarrow\ 5x = 90$
3
Divide both sides by 5:
$\frac{5x}{5} = \frac{90}{5} \ \Rightarrow\ x = 18$
4
Check: put x = 18 back into the equation.
$5\cdot18 - 12 = 90 - 12 = 78 \checkmark$

LaTeX source of the formulas on this page

\[ 5x - 12 = 78\ \Rightarrow\ x = 18 \]
\[ 5x - 12 = 78 \]
\[ 5x - 12 + 12 = 78 + 12 \ \Rightarrow\ 5x = 90 \]
\[ \frac{5x}{5} = \frac{90}{5} \ \Rightarrow\ x = 18 \]
\[ 5\cdot18 - 12 = 90 - 12 = 78 \checkmark \]

Trying values of x in 5x − 12 = 78

x	5x − 12	Equals 78?
16	68	no
17	73	no
18	78	yes
19	83	no
20	88	no

Questions

What is x in 5x − 12 = 78?

The solution of 5x − 12 = 78 is x = 18.

How do you solve 5x − 12 = 78?

Add 12 to both sides to get 5x = 90, then divide both sides by 5 to get x = 18.

How do I check the answer?

Replace x by 18: 5(18) − 12 = 78, which is 78.

Solve 5x − 12 = 78

How to work it out

Trying values of x in 5x − 12 = 78

Questions

Similar equations