x^2=8x-21

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


Simplifying
x2 = 8x + -21

Reorder the terms:
x2 = -21 + 8x

Solving
x2 = -21 + 8x

Solving for variable 'x'.

Reorder the terms:
21 + -8x + x2 = -21 + 8x + 21 + -8x

Reorder the terms:
21 + -8x + x2 = -21 + 21 + 8x + -8x

Combine like terms: -21 + 21 = 0
21 + -8x + x2 = 0 + 8x + -8x
21 + -8x + x2 = 8x + -8x

Combine like terms: 8x + -8x = 0
21 + -8x + x2 = 0

Begin completing the square.

Move the constant term to the right:

Add '-21' to each side of the equation.
21 + -8x + -21 + x2 = 0 + -21

Reorder the terms:
21 + -21 + -8x + x2 = 0 + -21

Combine like terms: 21 + -21 = 0
0 + -8x + x2 = 0 + -21
-8x + x2 = 0 + -21

Combine like terms: 0 + -21 = -21
-8x + x2 = -21

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

Add '16' to each side of the equation.
-8x + 16 + x2 = -21 + 16

Reorder the terms:
16 + -8x + x2 = -21 + 16

Combine like terms: -21 + 16 = -5
16 + -8x + x2 = -5

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

Can't calculate square root of the right side.

The solution to this equation could not be determined.

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