Solve 3x − 9 = 36

The solution of 3x − 9 = 36 is x = 15.

3x - 9 = 36\ \Rightarrow\ x = 15

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The lines y = 3x − 9 and y = 36 meet at x = 15. 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.
$3x - 9 = 36$
2
Add 9 to both sides:
$3x - 9 + 9 = 36 + 9 \ \Rightarrow\ 3x = 45$
3
Divide both sides by 3:
$\frac{3x}{3} = \frac{45}{3} \ \Rightarrow\ x = 15$
4
Check: put x = 15 back into the equation.
$3\cdot15 - 9 = 45 - 9 = 36 \checkmark$

LaTeX source of the formulas on this page

\[ 3x - 9 = 36\ \Rightarrow\ x = 15 \]
\[ 3x - 9 = 36 \]
\[ 3x - 9 + 9 = 36 + 9 \ \Rightarrow\ 3x = 45 \]
\[ \frac{3x}{3} = \frac{45}{3} \ \Rightarrow\ x = 15 \]
\[ 3\cdot15 - 9 = 45 - 9 = 36 \checkmark \]

Trying values of x in 3x − 9 = 36

x	3x − 9	Equals 36?
13	30	no
14	33	no
15	36	yes
16	39	no
17	42	no

Questions

What is x in 3x − 9 = 36?

The solution of 3x − 9 = 36 is x = 15.

How do you solve 3x − 9 = 36?

Add 9 to both sides to get 3x = 45, then divide both sides by 3 to get x = 15.

How do I check the answer?

Replace x by 15: 3(15) − 9 = 36, which is 36.

Solve 3x − 9 = 36

How to work it out

Trying values of x in 3x − 9 = 36

Questions

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