y^2-2y-15=3

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Solution for y^2-2y-15=3 equation:


Simplifying
y2 + -2y + -15 = 3

Reorder the terms:
-15 + -2y + y2 = 3

Solving
-15 + -2y + y2 = 3

Solving for variable 'y'.

Reorder the terms:
-15 + -3 + -2y + y2 = 3 + -3

Combine like terms: -15 + -3 = -18
-18 + -2y + y2 = 3 + -3

Combine like terms: 3 + -3 = 0
-18 + -2y + y2 = 0

Begin completing the square.

Move the constant term to the right:

Add '18' to each side of the equation.
-18 + -2y + 18 + y2 = 0 + 18

Reorder the terms:
-18 + 18 + -2y + y2 = 0 + 18

Combine like terms: -18 + 18 = 0
0 + -2y + y2 = 0 + 18
-2y + y2 = 0 + 18

Combine like terms: 0 + 18 = 18
-2y + y2 = 18

The y term is -2y.  Take half its coefficient (-1).
Square it (1) and add it to both sides.

Add '1' to each side of the equation.
-2y + 1 + y2 = 18 + 1

Reorder the terms:
1 + -2y + y2 = 18 + 1

Combine like terms: 18 + 1 = 19
1 + -2y + y2 = 19

Factor a perfect square on the left side:
(y + -1)(y + -1) = 19

Calculate the square root of the right side: 4.358898944

Break this problem into two subproblems by setting 
(y + -1) equal to 4.358898944 and -4.358898944.

Subproblem 1

y + -1 = 4.358898944 Simplifying y + -1 = 4.358898944 Reorder the terms: -1 + y = 4.358898944 Solving -1 + y = 4.358898944 Solving for variable 'y'. Move all terms containing y to the left, all other terms to the right. Add '1' to each side of the equation. -1 + 1 + y = 4.358898944 + 1 Combine like terms: -1 + 1 = 0 0 + y = 4.358898944 + 1 y = 4.358898944 + 1 Combine like terms: 4.358898944 + 1 = 5.358898944 y = 5.358898944 Simplifying y = 5.358898944

Subproblem 2

y + -1 = -4.358898944 Simplifying y + -1 = -4.358898944 Reorder the terms: -1 + y = -4.358898944 Solving -1 + y = -4.358898944 Solving for variable 'y'. Move all terms containing y to the left, all other terms to the right. Add '1' to each side of the equation. -1 + 1 + y = -4.358898944 + 1 Combine like terms: -1 + 1 = 0 0 + y = -4.358898944 + 1 y = -4.358898944 + 1 Combine like terms: -4.358898944 + 1 = -3.358898944 y = -3.358898944 Simplifying y = -3.358898944

Solution

The solution to the problem is based on the solutions from the subproblems. y = {5.358898944, -3.358898944}

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