a^2-8a=15

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Solution for a^2-8a=15 equation:


Simplifying
a2 + -8a = 15

Reorder the terms:
-8a + a2 = 15

Solving
-8a + a2 = 15

Solving for variable 'a'.

Reorder the terms:
-15 + -8a + a2 = 15 + -15

Combine like terms: 15 + -15 = 0
-15 + -8a + a2 = 0

Begin completing the square.

Move the constant term to the right:

Add '15' to each side of the equation.
-15 + -8a + 15 + a2 = 0 + 15

Reorder the terms:
-15 + 15 + -8a + a2 = 0 + 15

Combine like terms: -15 + 15 = 0
0 + -8a + a2 = 0 + 15
-8a + a2 = 0 + 15

Combine like terms: 0 + 15 = 15
-8a + a2 = 15

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 = 15 + 16

Reorder the terms:
16 + -8a + a2 = 15 + 16

Combine like terms: 15 + 16 = 31
16 + -8a + a2 = 31

Factor a perfect square on the left side:
(a + -4)(a + -4) = 31

Calculate the square root of the right side: 5.567764363

Break this problem into two subproblems by setting 
(a + -4) equal to 5.567764363 and -5.567764363.

Subproblem 1

a + -4 = 5.567764363 Simplifying a + -4 = 5.567764363 Reorder the terms: -4 + a = 5.567764363 Solving -4 + a = 5.567764363 Solving for variable 'a'. Move all terms containing a to the left, all other terms to the right. Add '4' to each side of the equation. -4 + 4 + a = 5.567764363 + 4 Combine like terms: -4 + 4 = 0 0 + a = 5.567764363 + 4 a = 5.567764363 + 4 Combine like terms: 5.567764363 + 4 = 9.567764363 a = 9.567764363 Simplifying a = 9.567764363

Subproblem 2

a + -4 = -5.567764363 Simplifying a + -4 = -5.567764363 Reorder the terms: -4 + a = -5.567764363 Solving -4 + a = -5.567764363 Solving for variable 'a'. Move all terms containing a to the left, all other terms to the right. Add '4' to each side of the equation. -4 + 4 + a = -5.567764363 + 4 Combine like terms: -4 + 4 = 0 0 + a = -5.567764363 + 4 a = -5.567764363 + 4 Combine like terms: -5.567764363 + 4 = -1.567764363 a = -1.567764363 Simplifying a = -1.567764363

Solution

The solution to the problem is based on the solutions from the subproblems. a = {9.567764363, -1.567764363}

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