y^2-y-15=0

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


Simplifying
y2 + -1y + -15 = 0

Reorder the terms:
-15 + -1y + y2 = 0

Solving
-15 + -1y + y2 = 0

Solving for variable 'y'.

Begin completing the square.

Move the constant term to the right:

Add '15' to each side of the equation.
-15 + -1y + 15 + y2 = 0 + 15

Reorder the terms:
-15 + 15 + -1y + y2 = 0 + 15

Combine like terms: -15 + 15 = 0
0 + -1y + y2 = 0 + 15
-1y + y2 = 0 + 15

Combine like terms: 0 + 15 = 15
-1y + y2 = 15

The y term is -1y.  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.
-1y + 0.25 + y2 = 15 + 0.25

Reorder the terms:
0.25 + -1y + y2 = 15 + 0.25

Combine like terms: 15 + 0.25 = 15.25
0.25 + -1y + y2 = 15.25

Factor a perfect square on the left side:
(y + -0.5)(y + -0.5) = 15.25

Calculate the square root of the right side: 3.905124838

Break this problem into two subproblems by setting 
(y + -0.5) equal to 3.905124838 and -3.905124838.

Subproblem 1

y + -0.5 = 3.905124838 Simplifying y + -0.5 = 3.905124838 Reorder the terms: -0.5 + y = 3.905124838 Solving -0.5 + y = 3.905124838 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 = 3.905124838 + 0.5 Combine like terms: -0.5 + 0.5 = 0.0 0.0 + y = 3.905124838 + 0.5 y = 3.905124838 + 0.5 Combine like terms: 3.905124838 + 0.5 = 4.405124838 y = 4.405124838 Simplifying y = 4.405124838

Subproblem 2

y + -0.5 = -3.905124838 Simplifying y + -0.5 = -3.905124838 Reorder the terms: -0.5 + y = -3.905124838 Solving -0.5 + y = -3.905124838 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 = -3.905124838 + 0.5 Combine like terms: -0.5 + 0.5 = 0.0 0.0 + y = -3.905124838 + 0.5 y = -3.905124838 + 0.5 Combine like terms: -3.905124838 + 0.5 = -3.405124838 y = -3.405124838 Simplifying y = -3.405124838

Solution

The solution to the problem is based on the solutions from the subproblems. y = {4.405124838, -3.405124838}

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