Solve 8x − 7 = 129

The solution of 8x − 7 = 129 is x = 17.

8x - 7 = 129\ \Rightarrow\ x = 17

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The lines y = 8x − 7 and y = 129 meet at x = 17. 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.
$8x - 7 = 129$
2
Add 7 to both sides:
$8x - 7 + 7 = 129 + 7 \ \Rightarrow\ 8x = 136$
3
Divide both sides by 8:
$\frac{8x}{8} = \frac{136}{8} \ \Rightarrow\ x = 17$
4
Check: put x = 17 back into the equation.
$8\cdot17 - 7 = 136 - 7 = 129 \checkmark$

LaTeX source of the formulas on this page

\[ 8x - 7 = 129\ \Rightarrow\ x = 17 \]
\[ 8x - 7 = 129 \]
\[ 8x - 7 + 7 = 129 + 7 \ \Rightarrow\ 8x = 136 \]
\[ \frac{8x}{8} = \frac{136}{8} \ \Rightarrow\ x = 17 \]
\[ 8\cdot17 - 7 = 136 - 7 = 129 \checkmark \]

Trying values of x in 8x − 7 = 129

x	8x − 7	Equals 129?
15	113	no
16	121	no
17	129	yes
18	137	no
19	145	no

Questions

What is x in 8x − 7 = 129?

The solution of 8x − 7 = 129 is x = 17.

How do you solve 8x − 7 = 129?

Add 7 to both sides to get 8x = 136, then divide both sides by 8 to get x = 17.

How do I check the answer?

Replace x by 17: 8(17) − 7 = 129, which is 129.

Solve 8x − 7 = 129

How to work it out

Trying values of x in 8x − 7 = 129

Questions

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