Solve 8x − 9 = 31

The solution of 8x − 9 = 31 is x = 5.

8x - 9 = 31\ \Rightarrow\ x = 5

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

The lines y = 8x − 9 and y = 31 meet at x = 5. 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.
$8x - 9 = 31$
2
Add 9 to both sides:
$8x - 9 + 9 = 31 + 9 \ \Rightarrow\ 8x = 40$
3
Divide both sides by 8:
$\frac{8x}{8} = \frac{40}{8} \ \Rightarrow\ x = 5$
4
Check: put x = 5 back into the equation.
$8\cdot5 - 9 = 40 - 9 = 31 \checkmark$

LaTeX source of the formulas on this page

\[ 8x - 9 = 31\ \Rightarrow\ x = 5 \]
\[ 8x - 9 = 31 \]
\[ 8x - 9 + 9 = 31 + 9 \ \Rightarrow\ 8x = 40 \]
\[ \frac{8x}{8} = \frac{40}{8} \ \Rightarrow\ x = 5 \]
\[ 8\cdot5 - 9 = 40 - 9 = 31 \checkmark \]

Trying values of x in 8x − 9 = 31

x	8x − 9	Equals 31?
3	15	no
4	23	no
5	31	yes
6	39	no
7	47	no

Questions

What is x in 8x − 9 = 31?

The solution of 8x − 9 = 31 is x = 5.

How do you solve 8x − 9 = 31?

Add 9 to both sides to get 8x = 40, then divide both sides by 8 to get x = 5.

How do I check the answer?

Replace x by 5: 8(5) − 9 = 31, which is 31.

Solve 8x − 9 = 31

How to work it out

Trying values of x in 8x − 9 = 31

Questions

Similar equations