Solve 3x − 15 = −21

The solution of 3x − 15 = −21 is x = -2.

3x - 15 = -21\ \Rightarrow\ x = -2

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The lines y = 3x − 15 and y = -21 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.
$3x - 15 = -21$
2
Add 15 to both sides:
$3x - 15 + 15 = -21 + 15 \ \Rightarrow\ 3x = -6$
3
Divide both sides by 3:
$\frac{3x}{3} = \frac{-6}{3} \ \Rightarrow\ x = -2$
4
Check: put x = -2 back into the equation.
$3\cdot(-2) - 15 = -6 - 15 = -21 \checkmark$

LaTeX source of the formulas on this page

\[ 3x - 15 = -21\ \Rightarrow\ x = -2 \]
\[ 3x - 15 = -21 \]
\[ 3x - 15 + 15 = -21 + 15 \ \Rightarrow\ 3x = -6 \]
\[ \frac{3x}{3} = \frac{-6}{3} \ \Rightarrow\ x = -2 \]
\[ 3\cdot(-2) - 15 = -6 - 15 = -21 \checkmark \]

Trying values of x in 3x − 15 = −21

x	3x − 15	Equals -21?
-4	-27	no
-3	-24	no
-2	-21	yes
-1	-18	no
0	-15	no

Questions

What is x in 3x − 15 = −21?

The solution of 3x − 15 = −21 is x = -2.

How do you solve 3x − 15 = −21?

Add 15 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) − 15 = -21, which is -21.

Solve 3x − 15 = −21

How to work it out

Trying values of x in 3x − 15 = −21

Questions

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