Solve 9x − 1 = 80

The solution of 9x − 1 = 80 is x = 9.

9x - 1 = 80\ \Rightarrow\ x = 9

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The lines y = 9x − 1 and y = 80 meet at x = 9. 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.
$9x - 1 = 80$
2
Add 1 to both sides:
$9x - 1 + 1 = 80 + 1 \ \Rightarrow\ 9x = 81$
3
Divide both sides by 9:
$\frac{9x}{9} = \frac{81}{9} \ \Rightarrow\ x = 9$
4
Check: put x = 9 back into the equation.
$9\cdot9 - 1 = 81 - 1 = 80 \checkmark$

LaTeX source of the formulas on this page

\[ 9x - 1 = 80\ \Rightarrow\ x = 9 \]
\[ 9x - 1 = 80 \]
\[ 9x - 1 + 1 = 80 + 1 \ \Rightarrow\ 9x = 81 \]
\[ \frac{9x}{9} = \frac{81}{9} \ \Rightarrow\ x = 9 \]
\[ 9\cdot9 - 1 = 81 - 1 = 80 \checkmark \]

Trying values of x in 9x − 1 = 80

x	9x − 1	Equals 80?
7	62	no
8	71	no
9	80	yes
10	89	no
11	98	no

Questions

What is x in 9x − 1 = 80?

The solution of 9x − 1 = 80 is x = 9.

How do you solve 9x − 1 = 80?

Add 1 to both sides to get 9x = 81, then divide both sides by 9 to get x = 9.

How do I check the answer?

Replace x by 9: 9(9) − 1 = 80, which is 80.

Solve 9x − 1 = 80

How to work it out

Trying values of x in 9x − 1 = 80

Questions

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