15y^2+y-81=0

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Solution for 15y^2+y-81=0 equation:


Simplifying
15y2 + y + -81 = 0

Reorder the terms:
-81 + y + 15y2 = 0

Solving
-81 + y + 15y2 = 0

Solving for variable 'y'.

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

Divide each side by '15'.
-5.4 + 0.06666666667y + y2 = 0

Move the constant term to the right:

Add '5.4' to each side of the equation.
-5.4 + 0.06666666667y + 5.4 + y2 = 0 + 5.4

Reorder the terms:
-5.4 + 5.4 + 0.06666666667y + y2 = 0 + 5.4

Combine like terms: -5.4 + 5.4 = 0.0
0.0 + 0.06666666667y + y2 = 0 + 5.4
0.06666666667y + y2 = 0 + 5.4

Combine like terms: 0 + 5.4 = 5.4
0.06666666667y + y2 = 5.4

The y term is y.  Take half its coefficient (0.5).
Square it (0.25) and add it to both sides.

Add '0.25' to each side of the equation.
0.06666666667y + 0.25 + y2 = 5.4 + 0.25

Reorder the terms:
0.25 + 0.06666666667y + y2 = 5.4 + 0.25

Combine like terms: 5.4 + 0.25 = 5.65
0.25 + 0.06666666667y + y2 = 5.65

Factor a perfect square on the left side:
(y + 0.5)(y + 0.5) = 5.65

Calculate the square root of the right side: 2.376972865

Break this problem into two subproblems by setting 
(y + 0.5) equal to 2.376972865 and -2.376972865.

Subproblem 1

y + 0.5 = 2.376972865 Simplifying y + 0.5 = 2.376972865 Reorder the terms: 0.5 + y = 2.376972865 Solving 0.5 + y = 2.376972865 Solving for variable 'y'. Move all terms containing y to the left, all other terms to the right. Add '-0.5' to each side of the equation. 0.5 + -0.5 + y = 2.376972865 + -0.5 Combine like terms: 0.5 + -0.5 = 0.0 0.0 + y = 2.376972865 + -0.5 y = 2.376972865 + -0.5 Combine like terms: 2.376972865 + -0.5 = 1.876972865 y = 1.876972865 Simplifying y = 1.876972865

Subproblem 2

y + 0.5 = -2.376972865 Simplifying y + 0.5 = -2.376972865 Reorder the terms: 0.5 + y = -2.376972865 Solving 0.5 + y = -2.376972865 Solving for variable 'y'. Move all terms containing y to the left, all other terms to the right. Add '-0.5' to each side of the equation. 0.5 + -0.5 + y = -2.376972865 + -0.5 Combine like terms: 0.5 + -0.5 = 0.0 0.0 + y = -2.376972865 + -0.5 y = -2.376972865 + -0.5 Combine like terms: -2.376972865 + -0.5 = -2.876972865 y = -2.876972865 Simplifying y = -2.876972865

Solution

The solution to the problem is based on the solutions from the subproblems. y = {1.876972865, -2.876972865}

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