2y^2+7y-81=0

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Solution for 2y^2+7y-81=0 equation:


Simplifying
2y2 + 7y + -81 = 0

Reorder the terms:
-81 + 7y + 2y2 = 0

Solving
-81 + 7y + 2y2 = 0

Solving for variable 'y'.

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

Divide each side by '2'.
-40.5 + 3.5y + y2 = 0

Move the constant term to the right:

Add '40.5' to each side of the equation.
-40.5 + 3.5y + 40.5 + y2 = 0 + 40.5

Reorder the terms:
-40.5 + 40.5 + 3.5y + y2 = 0 + 40.5

Combine like terms: -40.5 + 40.5 = 0.0
0.0 + 3.5y + y2 = 0 + 40.5
3.5y + y2 = 0 + 40.5

Combine like terms: 0 + 40.5 = 40.5
3.5y + y2 = 40.5

The y term is 3.5y.  Take half its coefficient (1.75).
Square it (3.0625) and add it to both sides.

Add '3.0625' to each side of the equation.
3.5y + 3.0625 + y2 = 40.5 + 3.0625

Reorder the terms:
3.0625 + 3.5y + y2 = 40.5 + 3.0625

Combine like terms: 40.5 + 3.0625 = 43.5625
3.0625 + 3.5y + y2 = 43.5625

Factor a perfect square on the left side:
(y + 1.75)(y + 1.75) = 43.5625

Calculate the square root of the right side: 6.600189391

Break this problem into two subproblems by setting 
(y + 1.75) equal to 6.600189391 and -6.600189391.

Subproblem 1

y + 1.75 = 6.600189391 Simplifying y + 1.75 = 6.600189391 Reorder the terms: 1.75 + y = 6.600189391 Solving 1.75 + y = 6.600189391 Solving for variable 'y'. Move all terms containing y to the left, all other terms to the right. Add '-1.75' to each side of the equation. 1.75 + -1.75 + y = 6.600189391 + -1.75 Combine like terms: 1.75 + -1.75 = 0.00 0.00 + y = 6.600189391 + -1.75 y = 6.600189391 + -1.75 Combine like terms: 6.600189391 + -1.75 = 4.850189391 y = 4.850189391 Simplifying y = 4.850189391

Subproblem 2

y + 1.75 = -6.600189391 Simplifying y + 1.75 = -6.600189391 Reorder the terms: 1.75 + y = -6.600189391 Solving 1.75 + y = -6.600189391 Solving for variable 'y'. Move all terms containing y to the left, all other terms to the right. Add '-1.75' to each side of the equation. 1.75 + -1.75 + y = -6.600189391 + -1.75 Combine like terms: 1.75 + -1.75 = 0.00 0.00 + y = -6.600189391 + -1.75 y = -6.600189391 + -1.75 Combine like terms: -6.600189391 + -1.75 = -8.350189391 y = -8.350189391 Simplifying y = -8.350189391

Solution

The solution to the problem is based on the solutions from the subproblems. y = {4.850189391, -8.350189391}

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