Solve 12x − 9 = 39

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

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

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The lines y = 12x − 9 and y = 39 meet at x = 4. 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.
$12x - 9 = 39$
2
Add 9 to both sides:
$12x - 9 + 9 = 39 + 9 \ \Rightarrow\ 12x = 48$
3
Divide both sides by 12:
$\frac{12x}{12} = \frac{48}{12} \ \Rightarrow\ x = 4$
4
Check: put x = 4 back into the equation.
$12\cdot4 - 9 = 48 - 9 = 39 \checkmark$

LaTeX source of the formulas on this page

\[ 12x - 9 = 39\ \Rightarrow\ x = 4 \]
\[ 12x - 9 = 39 \]
\[ 12x - 9 + 9 = 39 + 9 \ \Rightarrow\ 12x = 48 \]
\[ \frac{12x}{12} = \frac{48}{12} \ \Rightarrow\ x = 4 \]
\[ 12\cdot4 - 9 = 48 - 9 = 39 \checkmark \]

Trying values of x in 12x − 9 = 39

x	12x − 9	Equals 39?
2	15	no
3	27	no
4	39	yes
5	51	no
6	63	no

Questions

What is x in 12x − 9 = 39?

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

How do you solve 12x − 9 = 39?

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

How do I check the answer?

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

Solve 12x − 9 = 39

How to work it out

Trying values of x in 12x − 9 = 39

Questions

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