Solve 5x − 9 = 31

The solution of 5x − 9 = 31 is x = 8.

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

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The lines y = 5x − 9 and y = 31 meet at x = 8. 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.
$5x - 9 = 31$
2
Add 9 to both sides:
$5x - 9 + 9 = 31 + 9 \ \Rightarrow\ 5x = 40$
3
Divide both sides by 5:
$\frac{5x}{5} = \frac{40}{5} \ \Rightarrow\ x = 8$
4
Check: put x = 8 back into the equation.
$5\cdot8 - 9 = 40 - 9 = 31 \checkmark$

LaTeX source of the formulas on this page

\[ 5x - 9 = 31\ \Rightarrow\ x = 8 \]
\[ 5x - 9 = 31 \]
\[ 5x - 9 + 9 = 31 + 9 \ \Rightarrow\ 5x = 40 \]
\[ \frac{5x}{5} = \frac{40}{5} \ \Rightarrow\ x = 8 \]
\[ 5\cdot8 - 9 = 40 - 9 = 31 \checkmark \]

Trying values of x in 5x − 9 = 31

x	5x − 9	Equals 31?
6	21	no
7	26	no
8	31	yes
9	36	no
10	41	no

Questions

What is x in 5x − 9 = 31?

The solution of 5x − 9 = 31 is x = 8.

How do you solve 5x − 9 = 31?

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

How do I check the answer?

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

Solve 5x − 9 = 31

How to work it out

Trying values of x in 5x − 9 = 31

Questions

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