y^2-8y=-21

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Solution for y^2-8y=-21 equation:


Simplifying
y2 + -8y = -21

Reorder the terms:
-8y + y2 = -21

Solving
-8y + y2 = -21

Solving for variable 'y'.

Reorder the terms:
21 + -8y + y2 = -21 + 21

Combine like terms: -21 + 21 = 0
21 + -8y + y2 = 0

Begin completing the square.

Move the constant term to the right:

Add '-21' to each side of the equation.
21 + -8y + -21 + y2 = 0 + -21

Reorder the terms:
21 + -21 + -8y + y2 = 0 + -21

Combine like terms: 21 + -21 = 0
0 + -8y + y2 = 0 + -21
-8y + y2 = 0 + -21

Combine like terms: 0 + -21 = -21
-8y + y2 = -21

The y term is -8y.  Take half its coefficient (-4).
Square it (16) and add it to both sides.

Add '16' to each side of the equation.
-8y + 16 + y2 = -21 + 16

Reorder the terms:
16 + -8y + y2 = -21 + 16

Combine like terms: -21 + 16 = -5
16 + -8y + y2 = -5

Factor a perfect square on the left side:
(y + -4)(y + -4) = -5

Can't calculate square root of the right side.

The solution to this equation could not be determined.

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