y^2-2y=9

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Solution for y^2-2y=9 equation:


Simplifying
y2 + -2y = 9

Reorder the terms:
-2y + y2 = 9

Solving
-2y + y2 = 9

Solving for variable 'y'.

Reorder the terms:
-9 + -2y + y2 = 9 + -9

Combine like terms: 9 + -9 = 0
-9 + -2y + y2 = 0

Begin completing the square.

Move the constant term to the right:

Add '9' to each side of the equation.
-9 + -2y + 9 + y2 = 0 + 9

Reorder the terms:
-9 + 9 + -2y + y2 = 0 + 9

Combine like terms: -9 + 9 = 0
0 + -2y + y2 = 0 + 9
-2y + y2 = 0 + 9

Combine like terms: 0 + 9 = 9
-2y + y2 = 9

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 = 9 + 1

Reorder the terms:
1 + -2y + y2 = 9 + 1

Combine like terms: 9 + 1 = 10
1 + -2y + y2 = 10

Factor a perfect square on the left side:
(y + -1)(y + -1) = 10

Calculate the square root of the right side: 3.16227766

Break this problem into two subproblems by setting 
(y + -1) equal to 3.16227766 and -3.16227766.

Subproblem 1

y + -1 = 3.16227766 Simplifying y + -1 = 3.16227766 Reorder the terms: -1 + y = 3.16227766 Solving -1 + y = 3.16227766 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 = 3.16227766 + 1 Combine like terms: -1 + 1 = 0 0 + y = 3.16227766 + 1 y = 3.16227766 + 1 Combine like terms: 3.16227766 + 1 = 4.16227766 y = 4.16227766 Simplifying y = 4.16227766

Subproblem 2

y + -1 = -3.16227766 Simplifying y + -1 = -3.16227766 Reorder the terms: -1 + y = -3.16227766 Solving -1 + y = -3.16227766 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 = -3.16227766 + 1 Combine like terms: -1 + 1 = 0 0 + y = -3.16227766 + 1 y = -3.16227766 + 1 Combine like terms: -3.16227766 + 1 = -2.16227766 y = -2.16227766 Simplifying y = -2.16227766

Solution

The solution to the problem is based on the solutions from the subproblems. y = {4.16227766, -2.16227766}

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