Solve 4x − 9 = 39

The solution of 4x − 9 = 39 is x = 12.

4x - 9 = 39\ \Rightarrow\ x = 12

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

The lines y = 4x − 9 and y = 39 meet at x = 12. 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.
$4x - 9 = 39$
2
Add 9 to both sides:
$4x - 9 + 9 = 39 + 9 \ \Rightarrow\ 4x = 48$
3
Divide both sides by 4:
$\frac{4x}{4} = \frac{48}{4} \ \Rightarrow\ x = 12$
4
Check: put x = 12 back into the equation.
$4\cdot12 - 9 = 48 - 9 = 39 \checkmark$

LaTeX source of the formulas on this page

\[ 4x - 9 = 39\ \Rightarrow\ x = 12 \]
\[ 4x - 9 = 39 \]
\[ 4x - 9 + 9 = 39 + 9 \ \Rightarrow\ 4x = 48 \]
\[ \frac{4x}{4} = \frac{48}{4} \ \Rightarrow\ x = 12 \]
\[ 4\cdot12 - 9 = 48 - 9 = 39 \checkmark \]

Trying values of x in 4x − 9 = 39

x	4x − 9	Equals 39?
10	31	no
11	35	no
12	39	yes
13	43	no
14	47	no

Questions

What is x in 4x − 9 = 39?

The solution of 4x − 9 = 39 is x = 12.

How do you solve 4x − 9 = 39?

Add 9 to both sides to get 4x = 48, then divide both sides by 4 to get x = 12.

How do I check the answer?

Replace x by 12: 4(12) − 9 = 39, which is 39.

Solve 4x − 9 = 39

How to work it out

Trying values of x in 4x − 9 = 39

Questions

Similar equations