Solve 8x + 9 = −71

The solution of 8x + 9 = −71 is x = -10.

8x + 9 = -71\ \Rightarrow\ x = -10

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The lines y = 8x + 9 and y = -71 meet at x = -10. 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.
$8x + 9 = -71$
2
Subtract 9 from both sides:
$8x + 9 - 9 = -71 - 9 \ \Rightarrow\ 8x = -80$
3
Divide both sides by 8:
$\frac{8x}{8} = \frac{-80}{8} \ \Rightarrow\ x = -10$
4
Check: put x = -10 back into the equation.
$8\cdot(-10) + 9 = -80 + 9 = -71 \checkmark$

LaTeX source of the formulas on this page

\[ 8x + 9 = -71\ \Rightarrow\ x = -10 \]
\[ 8x + 9 = -71 \]
\[ 8x + 9 - 9 = -71 - 9 \ \Rightarrow\ 8x = -80 \]
\[ \frac{8x}{8} = \frac{-80}{8} \ \Rightarrow\ x = -10 \]
\[ 8\cdot(-10) + 9 = -80 + 9 = -71 \checkmark \]

Trying values of x in 8x + 9 = −71

x	8x + 9	Equals -71?
-12	-87	no
-11	-79	no
-10	-71	yes
-9	-63	no
-8	-55	no

Questions

What is x in 8x + 9 = −71?

The solution of 8x + 9 = −71 is x = -10.

How do you solve 8x + 9 = −71?

Subtract 9 from both sides to get 8x = -80, then divide both sides by 8 to get x = -10.

How do I check the answer?

Replace x by -10: 8(-10) + 9 = -71, which is -71.

Solve 8x + 9 = −71

How to work it out

Trying values of x in 8x + 9 = −71

Questions

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