y^2-4y=18

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Solution for y^2-4y=18 equation:


Simplifying
y2 + -4y = 18

Reorder the terms:
-4y + y2 = 18

Solving
-4y + y2 = 18

Solving for variable 'y'.

Reorder the terms:
-18 + -4y + y2 = 18 + -18

Combine like terms: 18 + -18 = 0
-18 + -4y + y2 = 0

Begin completing the square.

Move the constant term to the right:

Add '18' to each side of the equation.
-18 + -4y + 18 + y2 = 0 + 18

Reorder the terms:
-18 + 18 + -4y + y2 = 0 + 18

Combine like terms: -18 + 18 = 0
0 + -4y + y2 = 0 + 18
-4y + y2 = 0 + 18

Combine like terms: 0 + 18 = 18
-4y + y2 = 18

The y term is -4y.  Take half its coefficient (-2).
Square it (4) and add it to both sides.

Add '4' to each side of the equation.
-4y + 4 + y2 = 18 + 4

Reorder the terms:
4 + -4y + y2 = 18 + 4

Combine like terms: 18 + 4 = 22
4 + -4y + y2 = 22

Factor a perfect square on the left side:
(y + -2)(y + -2) = 22

Calculate the square root of the right side: 4.69041576

Break this problem into two subproblems by setting 
(y + -2) equal to 4.69041576 and -4.69041576.

Subproblem 1

y + -2 = 4.69041576 Simplifying y + -2 = 4.69041576 Reorder the terms: -2 + y = 4.69041576 Solving -2 + y = 4.69041576 Solving for variable 'y'. Move all terms containing y to the left, all other terms to the right. Add '2' to each side of the equation. -2 + 2 + y = 4.69041576 + 2 Combine like terms: -2 + 2 = 0 0 + y = 4.69041576 + 2 y = 4.69041576 + 2 Combine like terms: 4.69041576 + 2 = 6.69041576 y = 6.69041576 Simplifying y = 6.69041576

Subproblem 2

y + -2 = -4.69041576 Simplifying y + -2 = -4.69041576 Reorder the terms: -2 + y = -4.69041576 Solving -2 + y = -4.69041576 Solving for variable 'y'. Move all terms containing y to the left, all other terms to the right. Add '2' to each side of the equation. -2 + 2 + y = -4.69041576 + 2 Combine like terms: -2 + 2 = 0 0 + y = -4.69041576 + 2 y = -4.69041576 + 2 Combine like terms: -4.69041576 + 2 = -2.69041576 y = -2.69041576 Simplifying y = -2.69041576

Solution

The solution to the problem is based on the solutions from the subproblems. y = {6.69041576, -2.69041576}

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