Solve 8x − 9 = 87

The solution of 8x − 9 = 87 is x = 12.

8x - 9 = 87\ \Rightarrow\ x = 12

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The lines y = 8x − 9 and y = 87 meet at x = 12. 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.
$8x - 9 = 87$
2
Add 9 to both sides:
$8x - 9 + 9 = 87 + 9 \ \Rightarrow\ 8x = 96$
3
Divide both sides by 8:
$\frac{8x}{8} = \frac{96}{8} \ \Rightarrow\ x = 12$
4
Check: put x = 12 back into the equation.
$8\cdot12 - 9 = 96 - 9 = 87 \checkmark$

LaTeX source of the formulas on this page

\[ 8x - 9 = 87\ \Rightarrow\ x = 12 \]
\[ 8x - 9 = 87 \]
\[ 8x - 9 + 9 = 87 + 9 \ \Rightarrow\ 8x = 96 \]
\[ \frac{8x}{8} = \frac{96}{8} \ \Rightarrow\ x = 12 \]
\[ 8\cdot12 - 9 = 96 - 9 = 87 \checkmark \]

Trying values of x in 8x − 9 = 87

x	8x − 9	Equals 87?
10	71	no
11	79	no
12	87	yes
13	95	no
14	103	no

Questions

What is x in 8x − 9 = 87?

The solution of 8x − 9 = 87 is x = 12.

How do you solve 8x − 9 = 87?

Add 9 to both sides to get 8x = 96, then divide both sides by 8 to get x = 12.

How do I check the answer?

Replace x by 12: 8(12) − 9 = 87, which is 87.

Solve 8x − 9 = 87

How to work it out

Trying values of x in 8x − 9 = 87

Questions

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