Solve 8x + 9 = −15

The solution of 8x + 9 = −15 is x = -3.

8x + 9 = -15\ \Rightarrow\ x = -3

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The lines y = 8x + 9 and y = -15 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 addition, then the multiplication.
$8x + 9 = -15$
2
Subtract 9 from both sides:
$8x + 9 - 9 = -15 - 9 \ \Rightarrow\ 8x = -24$
3
Divide both sides by 8:
$\frac{8x}{8} = \frac{-24}{8} \ \Rightarrow\ x = -3$
4
Check: put x = -3 back into the equation.
$8\cdot(-3) + 9 = -24 + 9 = -15 \checkmark$

LaTeX source of the formulas on this page

\[ 8x + 9 = -15\ \Rightarrow\ x = -3 \]
\[ 8x + 9 = -15 \]
\[ 8x + 9 - 9 = -15 - 9 \ \Rightarrow\ 8x = -24 \]
\[ \frac{8x}{8} = \frac{-24}{8} \ \Rightarrow\ x = -3 \]
\[ 8\cdot(-3) + 9 = -24 + 9 = -15 \checkmark \]

Trying values of x in 8x + 9 = −15

x	8x + 9	Equals -15?
-5	-31	no
-4	-23	no
-3	-15	yes
-2	-7	no
-1	1	no

Questions

What is x in 8x + 9 = −15?

The solution of 8x + 9 = −15 is x = -3.

How do you solve 8x + 9 = −15?

Subtract 9 from both sides to get 8x = -24, then divide both sides by 8 to get x = -3.

How do I check the answer?

Replace x by -3: 8(-3) + 9 = -15, which is -15.

Solve 8x + 9 = −15

How to work it out

Trying values of x in 8x + 9 = −15

Questions

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