Solve 3x − 9 = 27

The solution of 3x − 9 = 27 is x = 12.

3x - 9 = 27\ \Rightarrow\ x = 12

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The lines y = 3x − 9 and y = 27 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.
$3x - 9 = 27$
2
Add 9 to both sides:
$3x - 9 + 9 = 27 + 9 \ \Rightarrow\ 3x = 36$
3
Divide both sides by 3:
$\frac{3x}{3} = \frac{36}{3} \ \Rightarrow\ x = 12$
4
Check: put x = 12 back into the equation.
$3\cdot12 - 9 = 36 - 9 = 27 \checkmark$

LaTeX source of the formulas on this page

\[ 3x - 9 = 27\ \Rightarrow\ x = 12 \]
\[ 3x - 9 = 27 \]
\[ 3x - 9 + 9 = 27 + 9 \ \Rightarrow\ 3x = 36 \]
\[ \frac{3x}{3} = \frac{36}{3} \ \Rightarrow\ x = 12 \]
\[ 3\cdot12 - 9 = 36 - 9 = 27 \checkmark \]

Trying values of x in 3x − 9 = 27

x	3x − 9	Equals 27?
10	21	no
11	24	no
12	27	yes
13	30	no
14	33	no

Questions

What is x in 3x − 9 = 27?

The solution of 3x − 9 = 27 is x = 12.

How do you solve 3x − 9 = 27?

Add 9 to both sides to get 3x = 36, then divide both sides by 3 to get x = 12.

How do I check the answer?

Replace x by 12: 3(12) − 9 = 27, which is 27.

Solve 3x − 9 = 27

How to work it out

Trying values of x in 3x − 9 = 27

Questions

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