Solve 9x + 15 = −66

The solution of 9x + 15 = −66 is x = -9.

9x + 15 = -66\ \Rightarrow\ x = -9

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The lines y = 9x + 15 and y = -66 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 addition, then the multiplication.
$9x + 15 = -66$
2
Subtract 15 from both sides:
$9x + 15 - 15 = -66 - 15 \ \Rightarrow\ 9x = -81$
3
Divide both sides by 9:
$\frac{9x}{9} = \frac{-81}{9} \ \Rightarrow\ x = -9$
4
Check: put x = -9 back into the equation.
$9\cdot(-9) + 15 = -81 + 15 = -66 \checkmark$

LaTeX source of the formulas on this page

\[ 9x + 15 = -66\ \Rightarrow\ x = -9 \]
\[ 9x + 15 = -66 \]
\[ 9x + 15 - 15 = -66 - 15 \ \Rightarrow\ 9x = -81 \]
\[ \frac{9x}{9} = \frac{-81}{9} \ \Rightarrow\ x = -9 \]
\[ 9\cdot(-9) + 15 = -81 + 15 = -66 \checkmark \]

Trying values of x in 9x + 15 = −66

x	9x + 15	Equals -66?
-11	-84	no
-10	-75	no
-9	-66	yes
-8	-57	no
-7	-48	no

Questions

What is x in 9x + 15 = −66?

The solution of 9x + 15 = −66 is x = -9.

How do you solve 9x + 15 = −66?

Subtract 15 from both sides to get 9x = -81, then divide both sides by 9 to get x = -9.

How do I check the answer?

Replace x by -9: 9(-9) + 15 = -66, which is -66.

Solve 9x + 15 = −66

How to work it out

Trying values of x in 9x + 15 = −66

Questions

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