5y^2-21=10y

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Solution for 5y^2-21=10y equation:


Simplifying
5y2 + -21 = 10y

Reorder the terms:
-21 + 5y2 = 10y

Solving
-21 + 5y2 = 10y

Solving for variable 'y'.

Reorder the terms:
-21 + -10y + 5y2 = 10y + -10y

Combine like terms: 10y + -10y = 0
-21 + -10y + 5y2 = 0

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

Divide each side by '5'.
-4.2 + -2y + y2 = 0

Move the constant term to the right:

Add '4.2' to each side of the equation.
-4.2 + -2y + 4.2 + y2 = 0 + 4.2

Reorder the terms:
-4.2 + 4.2 + -2y + y2 = 0 + 4.2

Combine like terms: -4.2 + 4.2 = 0.0
0.0 + -2y + y2 = 0 + 4.2
-2y + y2 = 0 + 4.2

Combine like terms: 0 + 4.2 = 4.2
-2y + y2 = 4.2

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 = 4.2 + 1

Reorder the terms:
1 + -2y + y2 = 4.2 + 1

Combine like terms: 4.2 + 1 = 5.2
1 + -2y + y2 = 5.2

Factor a perfect square on the left side:
(y + -1)(y + -1) = 5.2

Calculate the square root of the right side: 2.28035085

Break this problem into two subproblems by setting 
(y + -1) equal to 2.28035085 and -2.28035085.

Subproblem 1

y + -1 = 2.28035085 Simplifying y + -1 = 2.28035085 Reorder the terms: -1 + y = 2.28035085 Solving -1 + y = 2.28035085 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 = 2.28035085 + 1 Combine like terms: -1 + 1 = 0 0 + y = 2.28035085 + 1 y = 2.28035085 + 1 Combine like terms: 2.28035085 + 1 = 3.28035085 y = 3.28035085 Simplifying y = 3.28035085

Subproblem 2

y + -1 = -2.28035085 Simplifying y + -1 = -2.28035085 Reorder the terms: -1 + y = -2.28035085 Solving -1 + y = -2.28035085 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 = -2.28035085 + 1 Combine like terms: -1 + 1 = 0 0 + y = -2.28035085 + 1 y = -2.28035085 + 1 Combine like terms: -2.28035085 + 1 = -1.28035085 y = -1.28035085 Simplifying y = -1.28035085

Solution

The solution to the problem is based on the solutions from the subproblems. y = {3.28035085, -1.28035085}

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