a^2-8a+21=0

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Solution for a^2-8a+21=0 equation:


Simplifying
a2 + -8a + 21 = 0

Reorder the terms:
21 + -8a + a2 = 0

Solving
21 + -8a + a2 = 0

Solving for variable 'a'.

Begin completing the square.

Move the constant term to the right:

Add '-21' to each side of the equation.
21 + -8a + -21 + a2 = 0 + -21

Reorder the terms:
21 + -21 + -8a + a2 = 0 + -21

Combine like terms: 21 + -21 = 0
0 + -8a + a2 = 0 + -21
-8a + a2 = 0 + -21

Combine like terms: 0 + -21 = -21
-8a + a2 = -21

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

Add '16' to each side of the equation.
-8a + 16 + a2 = -21 + 16

Reorder the terms:
16 + -8a + a2 = -21 + 16

Combine like terms: -21 + 16 = -5
16 + -8a + a2 = -5

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

Can't calculate square root of the right side.

The solution to this equation could not be determined.

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