Solve 3x − 8 = 7

The solution of 3x − 8 = 7 is x = 5.

3x - 8 = 7\ \Rightarrow\ x = 5

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The lines y = 3x − 8 and y = 7 meet at x = 5. 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.
$3x - 8 = 7$
2
Add 8 to both sides:
$3x - 8 + 8 = 7 + 8 \ \Rightarrow\ 3x = 15$
3
Divide both sides by 3:
$\frac{3x}{3} = \frac{15}{3} \ \Rightarrow\ x = 5$
4
Check: put x = 5 back into the equation.
$3\cdot5 - 8 = 15 - 8 = 7 \checkmark$

LaTeX source of the formulas on this page

\[ 3x - 8 = 7\ \Rightarrow\ x = 5 \]
\[ 3x - 8 = 7 \]
\[ 3x - 8 + 8 = 7 + 8 \ \Rightarrow\ 3x = 15 \]
\[ \frac{3x}{3} = \frac{15}{3} \ \Rightarrow\ x = 5 \]
\[ 3\cdot5 - 8 = 15 - 8 = 7 \checkmark \]

Trying values of x in 3x − 8 = 7

x	3x − 8	Equals 7?
3	1	no
4	4	no
5	7	yes
6	10	no
7	13	no

Questions

What is x in 3x − 8 = 7?

The solution of 3x − 8 = 7 is x = 5.

How do you solve 3x − 8 = 7?

Add 8 to both sides to get 3x = 15, then divide both sides by 3 to get x = 5.

How do I check the answer?

Replace x by 5: 3(5) − 8 = 7, which is 7.

Solve 3x − 8 = 7

How to work it out

Trying values of x in 3x − 8 = 7

Questions

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