81-4r^2=0

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Solution for 81-4r^2=0 equation: 


Simplifying
81 + -4r2 = 0

Solving
81 + -4r2 = 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 + -4r2 = 0 + -81

Combine like terms: 81 + -81 = 0
0 + -4r2 = 0 + -81
-4r2 = 0 + -81

Combine like terms: 0 + -81 = -81
-4r2 = -81

Divide each side by '-4'.
r2 = 20.25

Simplifying
r2 = 20.25

Take the square root of each side:
r = {-4.5, 4.5}

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