Solve 4x − 9 = 31

The solution of 4x − 9 = 31 is x = 10.

4x - 9 = 31\ \Rightarrow\ x = 10

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The lines y = 4x − 9 and y = 31 meet at x = 10. 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.
$4x - 9 = 31$
2
Add 9 to both sides:
$4x - 9 + 9 = 31 + 9 \ \Rightarrow\ 4x = 40$
3
Divide both sides by 4:
$\frac{4x}{4} = \frac{40}{4} \ \Rightarrow\ x = 10$
4
Check: put x = 10 back into the equation.
$4\cdot10 - 9 = 40 - 9 = 31 \checkmark$

LaTeX source of the formulas on this page

\[ 4x - 9 = 31\ \Rightarrow\ x = 10 \]
\[ 4x - 9 = 31 \]
\[ 4x - 9 + 9 = 31 + 9 \ \Rightarrow\ 4x = 40 \]
\[ \frac{4x}{4} = \frac{40}{4} \ \Rightarrow\ x = 10 \]
\[ 4\cdot10 - 9 = 40 - 9 = 31 \checkmark \]

Trying values of x in 4x − 9 = 31

x	4x − 9	Equals 31?
8	23	no
9	27	no
10	31	yes
11	35	no
12	39	no

Questions

What is x in 4x − 9 = 31?

The solution of 4x − 9 = 31 is x = 10.

How do you solve 4x − 9 = 31?

Add 9 to both sides to get 4x = 40, then divide both sides by 4 to get x = 10.

How do I check the answer?

Replace x by 10: 4(10) − 9 = 31, which is 31.

Solve 4x − 9 = 31

How to work it out

Trying values of x in 4x − 9 = 31

Questions

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