a^2-15a-72=0

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Solution for a^2-15a-72=0 equation:


Simplifying
a2 + -15a + -72 = 0

Reorder the terms:
-72 + -15a + a2 = 0

Solving
-72 + -15a + a2 = 0

Solving for variable 'a'.

Begin completing the square.

Move the constant term to the right:

Add '72' to each side of the equation.
-72 + -15a + 72 + a2 = 0 + 72

Reorder the terms:
-72 + 72 + -15a + a2 = 0 + 72

Combine like terms: -72 + 72 = 0
0 + -15a + a2 = 0 + 72
-15a + a2 = 0 + 72

Combine like terms: 0 + 72 = 72
-15a + a2 = 72

The a term is -15a.  Take half its coefficient (-7.5).
Square it (56.25) and add it to both sides.

Add '56.25' to each side of the equation.
-15a + 56.25 + a2 = 72 + 56.25

Reorder the terms:
56.25 + -15a + a2 = 72 + 56.25

Combine like terms: 72 + 56.25 = 128.25
56.25 + -15a + a2 = 128.25

Factor a perfect square on the left side:
(a + -7.5)(a + -7.5) = 128.25

Calculate the square root of the right side: 11.324751653

Break this problem into two subproblems by setting 
(a + -7.5) equal to 11.324751653 and -11.324751653.

Subproblem 1

a + -7.5 = 11.324751653 Simplifying a + -7.5 = 11.324751653 Reorder the terms: -7.5 + a = 11.324751653 Solving -7.5 + a = 11.324751653 Solving for variable 'a'. Move all terms containing a to the left, all other terms to the right. Add '7.5' to each side of the equation. -7.5 + 7.5 + a = 11.324751653 + 7.5 Combine like terms: -7.5 + 7.5 = 0.0 0.0 + a = 11.324751653 + 7.5 a = 11.324751653 + 7.5 Combine like terms: 11.324751653 + 7.5 = 18.824751653 a = 18.824751653 Simplifying a = 18.824751653

Subproblem 2

a + -7.5 = -11.324751653 Simplifying a + -7.5 = -11.324751653 Reorder the terms: -7.5 + a = -11.324751653 Solving -7.5 + a = -11.324751653 Solving for variable 'a'. Move all terms containing a to the left, all other terms to the right. Add '7.5' to each side of the equation. -7.5 + 7.5 + a = -11.324751653 + 7.5 Combine like terms: -7.5 + 7.5 = 0.0 0.0 + a = -11.324751653 + 7.5 a = -11.324751653 + 7.5 Combine like terms: -11.324751653 + 7.5 = -3.824751653 a = -3.824751653 Simplifying a = -3.824751653

Solution

The solution to the problem is based on the solutions from the subproblems. a = {18.824751653, -3.824751653}

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