y^2-20y=90

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Solution for y^2-20y=90 equation:


Simplifying
y2 + -20y = 90

Reorder the terms:
-20y + y2 = 90

Solving
-20y + y2 = 90

Solving for variable 'y'.

Reorder the terms:
-90 + -20y + y2 = 90 + -90

Combine like terms: 90 + -90 = 0
-90 + -20y + y2 = 0

Begin completing the square.

Move the constant term to the right:

Add '90' to each side of the equation.
-90 + -20y + 90 + y2 = 0 + 90

Reorder the terms:
-90 + 90 + -20y + y2 = 0 + 90

Combine like terms: -90 + 90 = 0
0 + -20y + y2 = 0 + 90
-20y + y2 = 0 + 90

Combine like terms: 0 + 90 = 90
-20y + y2 = 90

The y term is -20y.  Take half its coefficient (-10).
Square it (100) and add it to both sides.

Add '100' to each side of the equation.
-20y + 100 + y2 = 90 + 100

Reorder the terms:
100 + -20y + y2 = 90 + 100

Combine like terms: 90 + 100 = 190
100 + -20y + y2 = 190

Factor a perfect square on the left side:
(y + -10)(y + -10) = 190

Calculate the square root of the right side: 13.784048752

Break this problem into two subproblems by setting 
(y + -10) equal to 13.784048752 and -13.784048752.

Subproblem 1

y + -10 = 13.784048752 Simplifying y + -10 = 13.784048752 Reorder the terms: -10 + y = 13.784048752 Solving -10 + y = 13.784048752 Solving for variable 'y'. Move all terms containing y to the left, all other terms to the right. Add '10' to each side of the equation. -10 + 10 + y = 13.784048752 + 10 Combine like terms: -10 + 10 = 0 0 + y = 13.784048752 + 10 y = 13.784048752 + 10 Combine like terms: 13.784048752 + 10 = 23.784048752 y = 23.784048752 Simplifying y = 23.784048752

Subproblem 2

y + -10 = -13.784048752 Simplifying y + -10 = -13.784048752 Reorder the terms: -10 + y = -13.784048752 Solving -10 + y = -13.784048752 Solving for variable 'y'. Move all terms containing y to the left, all other terms to the right. Add '10' to each side of the equation. -10 + 10 + y = -13.784048752 + 10 Combine like terms: -10 + 10 = 0 0 + y = -13.784048752 + 10 y = -13.784048752 + 10 Combine like terms: -13.784048752 + 10 = -3.784048752 y = -3.784048752 Simplifying y = -3.784048752

Solution

The solution to the problem is based on the solutions from the subproblems. y = {23.784048752, -3.784048752}

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