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 subtraction, then the multiplication.
$8x - 9 = 71$
2
Add 9 to 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.
$8\cdot10 - 9 = 80 - 9 = 71 \checkmark$

LaTeX source of the formulas on this page

\[ 8x - 9 = 71\ \Rightarrow\ x = 10 \]
\[ 8x - 9 = 71 \]
\[ 8x - 9 + 9 = 71 + 9 \ \Rightarrow\ 8x = 80 \]
\[ \frac{8x}{8} = \frac{80}{8} \ \Rightarrow\ x = 10 \]
\[ 8\cdot10 - 9 = 80 - 9 = 71 \checkmark \]

Trying values of x in 8x − 9 = 71

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

Add 9 to 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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