Solve 10x − 9 = 81

The solution of 10x − 9 = 81 is x = 9.

10x - 9 = 81\ \Rightarrow\ x = 9

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The lines y = 10x − 9 and y = 81 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.
$10x - 9 = 81$
2
Add 9 to both sides:
$10x - 9 + 9 = 81 + 9 \ \Rightarrow\ 10x = 90$
3
Divide both sides by 10:
$\frac{10x}{10} = \frac{90}{10} \ \Rightarrow\ x = 9$
4
Check: put x = 9 back into the equation.
$10\cdot9 - 9 = 90 - 9 = 81 \checkmark$

LaTeX source of the formulas on this page

\[ 10x - 9 = 81\ \Rightarrow\ x = 9 \]
\[ 10x - 9 = 81 \]
\[ 10x - 9 + 9 = 81 + 9 \ \Rightarrow\ 10x = 90 \]
\[ \frac{10x}{10} = \frac{90}{10} \ \Rightarrow\ x = 9 \]
\[ 10\cdot9 - 9 = 90 - 9 = 81 \checkmark \]

Trying values of x in 10x − 9 = 81

x	10x − 9	Equals 81?
7	61	no
8	71	no
9	81	yes
10	91	no
11	101	no

Questions

What is x in 10x − 9 = 81?

The solution of 10x − 9 = 81 is x = 9.

How do you solve 10x − 9 = 81?

Add 9 to both sides to get 10x = 90, then divide both sides by 10 to get x = 9.

How do I check the answer?

Replace x by 9: 10(9) − 9 = 81, which is 81.

Solve 10x − 9 = 81

How to work it out

Trying values of x in 10x − 9 = 81

Questions

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