Solve 4x − 9 = 71

The solution of 4x − 9 = 71 is x = 20.

4x - 9 = 71\ \Rightarrow\ x = 20

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

The lines y = 4x − 9 and y = 71 meet at x = 20. 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.
$4x - 9 = 71$
2
Add 9 to both sides:
$4x - 9 + 9 = 71 + 9 \ \Rightarrow\ 4x = 80$
3
Divide both sides by 4:
$\frac{4x}{4} = \frac{80}{4} \ \Rightarrow\ x = 20$
4
Check: put x = 20 back into the equation.
$4\cdot20 - 9 = 80 - 9 = 71 \checkmark$

LaTeX source of the formulas on this page

\[ 4x - 9 = 71\ \Rightarrow\ x = 20 \]
\[ 4x - 9 = 71 \]
\[ 4x - 9 + 9 = 71 + 9 \ \Rightarrow\ 4x = 80 \]
\[ \frac{4x}{4} = \frac{80}{4} \ \Rightarrow\ x = 20 \]
\[ 4\cdot20 - 9 = 80 - 9 = 71 \checkmark \]

Trying values of x in 4x − 9 = 71

x	4x − 9	Equals 71?
18	63	no
19	67	no
20	71	yes
21	75	no
22	79	no

Questions

What is x in 4x − 9 = 71?

The solution of 4x − 9 = 71 is x = 20.

How do you solve 4x − 9 = 71?

Add 9 to both sides to get 4x = 80, then divide both sides by 4 to get x = 20.

How do I check the answer?

Replace x by 20: 4(20) − 9 = 71, which is 71.

Solve 4x − 9 = 71

How to work it out

Trying values of x in 4x − 9 = 71

Questions

Similar equations