Solve 3x − 8 = 31

The solution of 3x − 8 = 31 is x = 13.

3x - 8 = 31\ \Rightarrow\ x = 13

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The lines y = 3x − 8 and y = 31 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.
$3x - 8 = 31$
2
Add 8 to both sides:
$3x - 8 + 8 = 31 + 8 \ \Rightarrow\ 3x = 39$
3
Divide both sides by 3:
$\frac{3x}{3} = \frac{39}{3} \ \Rightarrow\ x = 13$
4
Check: put x = 13 back into the equation.
$3\cdot13 - 8 = 39 - 8 = 31 \checkmark$

LaTeX source of the formulas on this page

\[ 3x - 8 = 31\ \Rightarrow\ x = 13 \]
\[ 3x - 8 = 31 \]
\[ 3x - 8 + 8 = 31 + 8 \ \Rightarrow\ 3x = 39 \]
\[ \frac{3x}{3} = \frac{39}{3} \ \Rightarrow\ x = 13 \]
\[ 3\cdot13 - 8 = 39 - 8 = 31 \checkmark \]

Trying values of x in 3x − 8 = 31

x	3x − 8	Equals 31?
11	25	no
12	28	no
13	31	yes
14	34	no
15	37	no

Questions

What is x in 3x − 8 = 31?

The solution of 3x − 8 = 31 is x = 13.

How do you solve 3x − 8 = 31?

Add 8 to both sides to get 3x = 39, then divide both sides by 3 to get x = 13.

How do I check the answer?

Replace x by 13: 3(13) − 8 = 31, which is 31.

Solve 3x − 8 = 31

How to work it out

Trying values of x in 3x − 8 = 31

Questions

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