Solve 9x − 15 = −42

The solution of 9x − 15 = −42 is x = -3.

9x - 15 = -42\ \Rightarrow\ x = -3

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The lines y = 9x − 15 and y = -42 meet at x = -3. 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.
$9x - 15 = -42$
2
Add 15 to both sides:
$9x - 15 + 15 = -42 + 15 \ \Rightarrow\ 9x = -27$
3
Divide both sides by 9:
$\frac{9x}{9} = \frac{-27}{9} \ \Rightarrow\ x = -3$
4
Check: put x = -3 back into the equation.
$9\cdot(-3) - 15 = -27 - 15 = -42 \checkmark$

LaTeX source of the formulas on this page

\[ 9x - 15 = -42\ \Rightarrow\ x = -3 \]
\[ 9x - 15 = -42 \]
\[ 9x - 15 + 15 = -42 + 15 \ \Rightarrow\ 9x = -27 \]
\[ \frac{9x}{9} = \frac{-27}{9} \ \Rightarrow\ x = -3 \]
\[ 9\cdot(-3) - 15 = -27 - 15 = -42 \checkmark \]

Trying values of x in 9x − 15 = −42

x	9x − 15	Equals -42?
-5	-60	no
-4	-51	no
-3	-42	yes
-2	-33	no
-1	-24	no

Questions

What is x in 9x − 15 = −42?

The solution of 9x − 15 = −42 is x = -3.

How do you solve 9x − 15 = −42?

Add 15 to both sides to get 9x = -27, then divide both sides by 9 to get x = -3.

How do I check the answer?

Replace x by -3: 9(-3) − 15 = -42, which is -42.

Solve 9x − 15 = −42

How to work it out

Trying values of x in 9x − 15 = −42

Questions

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