Solve 5x − 9 = 66

The solution of 5x − 9 = 66 is x = 15.

5x - 9 = 66\ \Rightarrow\ x = 15

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The lines y = 5x − 9 and y = 66 meet at x = 15. 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.
$5x - 9 = 66$
2
Add 9 to both sides:
$5x - 9 + 9 = 66 + 9 \ \Rightarrow\ 5x = 75$
3
Divide both sides by 5:
$\frac{5x}{5} = \frac{75}{5} \ \Rightarrow\ x = 15$
4
Check: put x = 15 back into the equation.
$5\cdot15 - 9 = 75 - 9 = 66 \checkmark$

LaTeX source of the formulas on this page

\[ 5x - 9 = 66\ \Rightarrow\ x = 15 \]
\[ 5x - 9 = 66 \]
\[ 5x - 9 + 9 = 66 + 9 \ \Rightarrow\ 5x = 75 \]
\[ \frac{5x}{5} = \frac{75}{5} \ \Rightarrow\ x = 15 \]
\[ 5\cdot15 - 9 = 75 - 9 = 66 \checkmark \]

Trying values of x in 5x − 9 = 66

x	5x − 9	Equals 66?
13	56	no
14	61	no
15	66	yes
16	71	no
17	76	no

Questions

What is x in 5x − 9 = 66?

The solution of 5x − 9 = 66 is x = 15.

How do you solve 5x − 9 = 66?

Add 9 to both sides to get 5x = 75, then divide both sides by 5 to get x = 15.

How do I check the answer?

Replace x by 15: 5(15) − 9 = 66, which is 66.

Solve 5x − 9 = 66

How to work it out

Trying values of x in 5x − 9 = 66

Questions

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