Solve 8x − 9 = 15

The solution of 8x − 9 = 15 is x = 3.

8x - 9 = 15\ \Rightarrow\ x = 3

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The lines y = 8x − 9 and y = 15 meet at x = 3. 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.
$8x - 9 = 15$
2
Add 9 to both sides:
$8x - 9 + 9 = 15 + 9 \ \Rightarrow\ 8x = 24$
3
Divide both sides by 8:
$\frac{8x}{8} = \frac{24}{8} \ \Rightarrow\ x = 3$
4
Check: put x = 3 back into the equation.
$8\cdot3 - 9 = 24 - 9 = 15 \checkmark$

LaTeX source of the formulas on this page

\[ 8x - 9 = 15\ \Rightarrow\ x = 3 \]
\[ 8x - 9 = 15 \]
\[ 8x - 9 + 9 = 15 + 9 \ \Rightarrow\ 8x = 24 \]
\[ \frac{8x}{8} = \frac{24}{8} \ \Rightarrow\ x = 3 \]
\[ 8\cdot3 - 9 = 24 - 9 = 15 \checkmark \]

Trying values of x in 8x − 9 = 15

x	8x − 9	Equals 15?
1	-1	no
2	7	no
3	15	yes
4	23	no
5	31	no

Questions

What is x in 8x − 9 = 15?

The solution of 8x − 9 = 15 is x = 3.

How do you solve 8x − 9 = 15?

Add 9 to both sides to get 8x = 24, then divide both sides by 8 to get x = 3.

How do I check the answer?

Replace x by 3: 8(3) − 9 = 15, which is 15.

Solve 8x − 9 = 15

How to work it out

Trying values of x in 8x − 9 = 15

Questions

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