2r-r^2=15

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Solution for 2r-r^2=15 equation:


Simplifying
2r + -1r2 = 15

Solving
2r + -1r2 = 15

Solving for variable 'r'.

Reorder the terms:
-15 + 2r + -1r2 = 15 + -15

Combine like terms: 15 + -15 = 0
-15 + 2r + -1r2 = 0

Begin completing the square.  Divide all terms by
-1 the coefficient of the squared term: 

Divide each side by '-1'.
15 + -2r + r2 = 0

Move the constant term to the right:

Add '-15' to each side of the equation.
15 + -2r + -15 + r2 = 0 + -15

Reorder the terms:
15 + -15 + -2r + r2 = 0 + -15

Combine like terms: 15 + -15 = 0
0 + -2r + r2 = 0 + -15
-2r + r2 = 0 + -15

Combine like terms: 0 + -15 = -15
-2r + r2 = -15

The r term is -2r.  Take half its coefficient (-1).
Square it (1) and add it to both sides.

Add '1' to each side of the equation.
-2r + 1 + r2 = -15 + 1

Reorder the terms:
1 + -2r + r2 = -15 + 1

Combine like terms: -15 + 1 = -14
1 + -2r + r2 = -14

Factor a perfect square on the left side:
(r + -1)(r + -1) = -14

Can't calculate square root of the right side.

The solution to this equation could not be determined.

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