r^2-81=

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Solution for r^2-81= equation: 


Simplifying
r2 + -81 = 0

Reorder the terms:
-81 + r2 = 0

Solving
-81 + r2 = 0

Solving for variable 'r'.

Move all terms containing r to the left, all other terms to the right.

Add '81' to each side of the equation.
-81 + 81 + r2 = 0 + 81

Combine like terms: -81 + 81 = 0
0 + r2 = 0 + 81
r2 = 0 + 81

Combine like terms: 0 + 81 = 81
r2 = 81

Simplifying
r2 = 81

Take the square root of each side:
r = {-9, 9}

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