y^2+2y-84=0

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Solution for y^2+2y-84=0 equation:


Simplifying
y2 + 2y + -84 = 0

Reorder the terms:
-84 + 2y + y2 = 0

Solving
-84 + 2y + y2 = 0

Solving for variable 'y'.

Begin completing the square.

Move the constant term to the right:

Add '84' to each side of the equation.
-84 + 2y + 84 + y2 = 0 + 84

Reorder the terms:
-84 + 84 + 2y + y2 = 0 + 84

Combine like terms: -84 + 84 = 0
0 + 2y + y2 = 0 + 84
2y + y2 = 0 + 84

Combine like terms: 0 + 84 = 84
2y + y2 = 84

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 = 84 + 1

Reorder the terms:
1 + 2y + y2 = 84 + 1

Combine like terms: 84 + 1 = 85
1 + 2y + y2 = 85

Factor a perfect square on the left side:
(y + 1)(y + 1) = 85

Calculate the square root of the right side: 9.219544457

Break this problem into two subproblems by setting 
(y + 1) equal to 9.219544457 and -9.219544457.

Subproblem 1

y + 1 = 9.219544457 Simplifying y + 1 = 9.219544457 Reorder the terms: 1 + y = 9.219544457 Solving 1 + y = 9.219544457 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 = 9.219544457 + -1 Combine like terms: 1 + -1 = 0 0 + y = 9.219544457 + -1 y = 9.219544457 + -1 Combine like terms: 9.219544457 + -1 = 8.219544457 y = 8.219544457 Simplifying y = 8.219544457

Subproblem 2

y + 1 = -9.219544457 Simplifying y + 1 = -9.219544457 Reorder the terms: 1 + y = -9.219544457 Solving 1 + y = -9.219544457 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 = -9.219544457 + -1 Combine like terms: 1 + -1 = 0 0 + y = -9.219544457 + -1 y = -9.219544457 + -1 Combine like terms: -9.219544457 + -1 = -10.219544457 y = -10.219544457 Simplifying y = -10.219544457

Solution

The solution to the problem is based on the solutions from the subproblems. y = {8.219544457, -10.219544457}

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