8y^2+9y-15=0

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Solution for 8y^2+9y-15=0 equation:


Simplifying
8y2 + 9y + -15 = 0

Reorder the terms:
-15 + 9y + 8y2 = 0

Solving
-15 + 9y + 8y2 = 0

Solving for variable 'y'.

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

Divide each side by '8'.
-1.875 + 1.125y + y2 = 0

Move the constant term to the right:

Add '1.875' to each side of the equation.
-1.875 + 1.125y + 1.875 + y2 = 0 + 1.875

Reorder the terms:
-1.875 + 1.875 + 1.125y + y2 = 0 + 1.875

Combine like terms: -1.875 + 1.875 = 0.000
0.000 + 1.125y + y2 = 0 + 1.875
1.125y + y2 = 0 + 1.875

Combine like terms: 0 + 1.875 = 1.875
1.125y + y2 = 1.875

The y term is 1.125y.  Take half its coefficient (0.5625).
Square it (0.31640625) and add it to both sides.

Add '0.31640625' to each side of the equation.
1.125y + 0.31640625 + y2 = 1.875 + 0.31640625

Reorder the terms:
0.31640625 + 1.125y + y2 = 1.875 + 0.31640625

Combine like terms: 1.875 + 0.31640625 = 2.19140625
0.31640625 + 1.125y + y2 = 2.19140625

Factor a perfect square on the left side:
(y + 0.5625)(y + 0.5625) = 2.19140625

Calculate the square root of the right side: 1.48033991

Break this problem into two subproblems by setting 
(y + 0.5625) equal to 1.48033991 and -1.48033991.

Subproblem 1

y + 0.5625 = 1.48033991 Simplifying y + 0.5625 = 1.48033991 Reorder the terms: 0.5625 + y = 1.48033991 Solving 0.5625 + y = 1.48033991 Solving for variable 'y'. Move all terms containing y to the left, all other terms to the right. Add '-0.5625' to each side of the equation. 0.5625 + -0.5625 + y = 1.48033991 + -0.5625 Combine like terms: 0.5625 + -0.5625 = 0.0000 0.0000 + y = 1.48033991 + -0.5625 y = 1.48033991 + -0.5625 Combine like terms: 1.48033991 + -0.5625 = 0.91783991 y = 0.91783991 Simplifying y = 0.91783991

Subproblem 2

y + 0.5625 = -1.48033991 Simplifying y + 0.5625 = -1.48033991 Reorder the terms: 0.5625 + y = -1.48033991 Solving 0.5625 + y = -1.48033991 Solving for variable 'y'. Move all terms containing y to the left, all other terms to the right. Add '-0.5625' to each side of the equation. 0.5625 + -0.5625 + y = -1.48033991 + -0.5625 Combine like terms: 0.5625 + -0.5625 = 0.0000 0.0000 + y = -1.48033991 + -0.5625 y = -1.48033991 + -0.5625 Combine like terms: -1.48033991 + -0.5625 = -2.04283991 y = -2.04283991 Simplifying y = -2.04283991

Solution

The solution to the problem is based on the solutions from the subproblems. y = {0.91783991, -2.04283991}

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