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Simplifying
f2 + 9f + -81 = 9f
Reorder the terms:
-81 + 9f + f2 = 9f
Add '-9f' to each side of the equation.
-81 + 9f + -9f + f2 = 9f + -9f
Combine like terms: 9f + -9f = 0
-81 + 0 + f2 = 9f + -9f
-81 + f2 = 9f + -9f
Combine like terms: 9f + -9f = 0
-81 + f2 = 0
Solving
-81 + f2 = 0
Solving for variable 'f'.
Move all terms containing f to the left, all other terms to the right.
Add '81' to each side of the equation.
-81 + 81 + f2 = 0 + 81
Combine like terms: -81 + 81 = 0
0 + f2 = 0 + 81
f2 = 0 + 81
Combine like terms: 0 + 81 = 81
f2 = 81
Simplifying
f2 = 81
Take the square root of each side:
f = {-9, 9}
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