Solve 3x − 9 = −15

The solution of 3x − 9 = −15 is x = -2.

3x - 9 = -15\ \Rightarrow\ x = -2

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

The lines y = 3x − 9 and y = -15 meet at x = -2. 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.
$3x - 9 = -15$
2
Add 9 to both sides:
$3x - 9 + 9 = -15 + 9 \ \Rightarrow\ 3x = -6$
3
Divide both sides by 3:
$\frac{3x}{3} = \frac{-6}{3} \ \Rightarrow\ x = -2$
4
Check: put x = -2 back into the equation.
$3\cdot(-2) - 9 = -6 - 9 = -15 \checkmark$

LaTeX source of the formulas on this page

\[ 3x - 9 = -15\ \Rightarrow\ x = -2 \]
\[ 3x - 9 = -15 \]
\[ 3x - 9 + 9 = -15 + 9 \ \Rightarrow\ 3x = -6 \]
\[ \frac{3x}{3} = \frac{-6}{3} \ \Rightarrow\ x = -2 \]
\[ 3\cdot(-2) - 9 = -6 - 9 = -15 \checkmark \]

Trying values of x in 3x − 9 = −15

x	3x − 9	Equals -15?
-4	-21	no
-3	-18	no
-2	-15	yes
-1	-12	no
0	-9	no

Questions

What is x in 3x − 9 = −15?

The solution of 3x − 9 = −15 is x = -2.

How do you solve 3x − 9 = −15?

Add 9 to both sides to get 3x = -6, then divide both sides by 3 to get x = -2.

How do I check the answer?

Replace x by -2: 3(-2) − 9 = -15, which is -15.

Solve 3x − 9 = −15

How to work it out

Trying values of x in 3x − 9 = −15

Questions

Similar equations