Solve 3x − 13 = −40

The solution of 3x − 13 = −40 is x = -9.

3x - 13 = -40\ \Rightarrow\ x = -9

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The lines y = 3x − 13 and y = -40 meet at x = -9. 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.
$3x - 13 = -40$
2
Add 13 to both sides:
$3x - 13 + 13 = -40 + 13 \ \Rightarrow\ 3x = -27$
3
Divide both sides by 3:
$\frac{3x}{3} = \frac{-27}{3} \ \Rightarrow\ x = -9$
4
Check: put x = -9 back into the equation.
$3\cdot(-9) - 13 = -27 - 13 = -40 \checkmark$

LaTeX source of the formulas on this page

\[ 3x - 13 = -40\ \Rightarrow\ x = -9 \]
\[ 3x - 13 = -40 \]
\[ 3x - 13 + 13 = -40 + 13 \ \Rightarrow\ 3x = -27 \]
\[ \frac{3x}{3} = \frac{-27}{3} \ \Rightarrow\ x = -9 \]
\[ 3\cdot(-9) - 13 = -27 - 13 = -40 \checkmark \]

Trying values of x in 3x − 13 = −40

x	3x − 13	Equals -40?
-11	-46	no
-10	-43	no
-9	-40	yes
-8	-37	no
-7	-34	no

Questions

What is x in 3x − 13 = −40?

The solution of 3x − 13 = −40 is x = -9.

How do you solve 3x − 13 = −40?

Add 13 to both sides to get 3x = -27, then divide both sides by 3 to get x = -9.

How do I check the answer?

Replace x by -9: 3(-9) − 13 = -40, which is -40.

Solve 3x − 13 = −40

How to work it out

Trying values of x in 3x − 13 = −40

Questions

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