r^2-4r+21=

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Solution for r^2-4r+21= equation:


Simplifying
r2 + -4r + 21 = 0

Reorder the terms:
21 + -4r + r2 = 0

Solving
21 + -4r + r2 = 0

Solving for variable 'r'.

Begin completing the square.

Move the constant term to the right:

Add '-21' to each side of the equation.
21 + -4r + -21 + r2 = 0 + -21

Reorder the terms:
21 + -21 + -4r + r2 = 0 + -21

Combine like terms: 21 + -21 = 0
0 + -4r + r2 = 0 + -21
-4r + r2 = 0 + -21

Combine like terms: 0 + -21 = -21
-4r + r2 = -21

The r term is -4r.  Take half its coefficient (-2).
Square it (4) and add it to both sides.

Add '4' to each side of the equation.
-4r + 4 + r2 = -21 + 4

Reorder the terms:
4 + -4r + r2 = -21 + 4

Combine like terms: -21 + 4 = -17
4 + -4r + r2 = -17

Factor a perfect square on the left side:
(r + -2)(r + -2) = -17

Can't calculate square root of the right side.

The solution to this equation could not be determined.

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