0=y^2-20y+21

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Solution for 0=y^2-20y+21 equation:


Simplifying
0 = y2 + -20y + 21

Reorder the terms:
0 = 21 + -20y + y2

Solving
0 = 21 + -20y + y2

Solving for variable 'y'.

Combine like terms: 0 + -21 = -21
-21 + 20y + -1y2 = 21 + -20y + y2 + -21 + 20y + -1y2

Reorder the terms:
-21 + 20y + -1y2 = 21 + -21 + -20y + 20y + y2 + -1y2

Combine like terms: 21 + -21 = 0
-21 + 20y + -1y2 = 0 + -20y + 20y + y2 + -1y2
-21 + 20y + -1y2 = -20y + 20y + y2 + -1y2

Combine like terms: -20y + 20y = 0
-21 + 20y + -1y2 = 0 + y2 + -1y2
-21 + 20y + -1y2 = y2 + -1y2

Combine like terms: y2 + -1y2 = 0
-21 + 20y + -1y2 = 0

Begin completing the square.  Divide all terms by
-1 the coefficient of the squared term: 

Divide each side by '-1'.
21 + -20y + y2 = 0

Move the constant term to the right:

Add '-21' to each side of the equation.
21 + -20y + -21 + y2 = 0 + -21

Reorder the terms:
21 + -21 + -20y + y2 = 0 + -21

Combine like terms: 21 + -21 = 0
0 + -20y + y2 = 0 + -21
-20y + y2 = 0 + -21

Combine like terms: 0 + -21 = -21
-20y + y2 = -21

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 = -21 + 100

Reorder the terms:
100 + -20y + y2 = -21 + 100

Combine like terms: -21 + 100 = 79
100 + -20y + y2 = 79

Factor a perfect square on the left side:
(y + -10)(y + -10) = 79

Calculate the square root of the right side: 8.888194417

Break this problem into two subproblems by setting 
(y + -10) equal to 8.888194417 and -8.888194417.

Subproblem 1

y + -10 = 8.888194417 Simplifying y + -10 = 8.888194417 Reorder the terms: -10 + y = 8.888194417 Solving -10 + y = 8.888194417 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 = 8.888194417 + 10 Combine like terms: -10 + 10 = 0 0 + y = 8.888194417 + 10 y = 8.888194417 + 10 Combine like terms: 8.888194417 + 10 = 18.888194417 y = 18.888194417 Simplifying y = 18.888194417

Subproblem 2

y + -10 = -8.888194417 Simplifying y + -10 = -8.888194417 Reorder the terms: -10 + y = -8.888194417 Solving -10 + y = -8.888194417 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 = -8.888194417 + 10 Combine like terms: -10 + 10 = 0 0 + y = -8.888194417 + 10 y = -8.888194417 + 10 Combine like terms: -8.888194417 + 10 = 1.111805583 y = 1.111805583 Simplifying y = 1.111805583

Solution

The solution to the problem is based on the solutions from the subproblems. y = {18.888194417, 1.111805583}

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