5a^2-8a=15

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Solution for 5a^2-8a=15 equation:


Simplifying
5a2 + -8a = 15

Reorder the terms:
-8a + 5a2 = 15

Solving
-8a + 5a2 = 15

Solving for variable 'a'.

Reorder the terms:
-15 + -8a + 5a2 = 15 + -15

Combine like terms: 15 + -15 = 0
-15 + -8a + 5a2 = 0

Begin completing the square.  Divide all terms by
5 the coefficient of the squared term: 

Divide each side by '5'.
-3 + -1.6a + a2 = 0

Move the constant term to the right:

Add '3' to each side of the equation.
-3 + -1.6a + 3 + a2 = 0 + 3

Reorder the terms:
-3 + 3 + -1.6a + a2 = 0 + 3

Combine like terms: -3 + 3 = 0
0 + -1.6a + a2 = 0 + 3
-1.6a + a2 = 0 + 3

Combine like terms: 0 + 3 = 3
-1.6a + a2 = 3

The a term is -1.6a.  Take half its coefficient (-0.8).
Square it (0.64) and add it to both sides.

Add '0.64' to each side of the equation.
-1.6a + 0.64 + a2 = 3 + 0.64

Reorder the terms:
0.64 + -1.6a + a2 = 3 + 0.64

Combine like terms: 3 + 0.64 = 3.64
0.64 + -1.6a + a2 = 3.64

Factor a perfect square on the left side:
(a + -0.8)(a + -0.8) = 3.64

Calculate the square root of the right side: 1.907878403

Break this problem into two subproblems by setting 
(a + -0.8) equal to 1.907878403 and -1.907878403.

Subproblem 1

a + -0.8 = 1.907878403 Simplifying a + -0.8 = 1.907878403 Reorder the terms: -0.8 + a = 1.907878403 Solving -0.8 + a = 1.907878403 Solving for variable 'a'. Move all terms containing a to the left, all other terms to the right. Add '0.8' to each side of the equation. -0.8 + 0.8 + a = 1.907878403 + 0.8 Combine like terms: -0.8 + 0.8 = 0.0 0.0 + a = 1.907878403 + 0.8 a = 1.907878403 + 0.8 Combine like terms: 1.907878403 + 0.8 = 2.707878403 a = 2.707878403 Simplifying a = 2.707878403

Subproblem 2

a + -0.8 = -1.907878403 Simplifying a + -0.8 = -1.907878403 Reorder the terms: -0.8 + a = -1.907878403 Solving -0.8 + a = -1.907878403 Solving for variable 'a'. Move all terms containing a to the left, all other terms to the right. Add '0.8' to each side of the equation. -0.8 + 0.8 + a = -1.907878403 + 0.8 Combine like terms: -0.8 + 0.8 = 0.0 0.0 + a = -1.907878403 + 0.8 a = -1.907878403 + 0.8 Combine like terms: -1.907878403 + 0.8 = -1.107878403 a = -1.107878403 Simplifying a = -1.107878403

Solution

The solution to the problem is based on the solutions from the subproblems. a = {2.707878403, -1.107878403}

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