Solve 7x − 12 = 128

The solution of 7x − 12 = 128 is x = 20.

7x - 12 = 128\ \Rightarrow\ x = 20

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The lines y = 7x − 12 and y = 128 meet at x = 20. 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.
$7x - 12 = 128$
2
Add 12 to both sides:
$7x - 12 + 12 = 128 + 12 \ \Rightarrow\ 7x = 140$
3
Divide both sides by 7:
$\frac{7x}{7} = \frac{140}{7} \ \Rightarrow\ x = 20$
4
Check: put x = 20 back into the equation.
$7\cdot20 - 12 = 140 - 12 = 128 \checkmark$

LaTeX source of the formulas on this page

\[ 7x - 12 = 128\ \Rightarrow\ x = 20 \]
\[ 7x - 12 = 128 \]
\[ 7x - 12 + 12 = 128 + 12 \ \Rightarrow\ 7x = 140 \]
\[ \frac{7x}{7} = \frac{140}{7} \ \Rightarrow\ x = 20 \]
\[ 7\cdot20 - 12 = 140 - 12 = 128 \checkmark \]

Trying values of x in 7x − 12 = 128

x	7x − 12	Equals 128?
18	114	no
19	121	no
20	128	yes
21	135	no
22	142	no

Questions

What is x in 7x − 12 = 128?

The solution of 7x − 12 = 128 is x = 20.

How do you solve 7x − 12 = 128?

Add 12 to both sides to get 7x = 140, then divide both sides by 7 to get x = 20.

How do I check the answer?

Replace x by 20: 7(20) − 12 = 128, which is 128.

Solve 7x − 12 = 128

How to work it out

Trying values of x in 7x − 12 = 128

Questions

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