y^2-4y=7

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Solution for y^2-4y=7 equation:


Simplifying
y2 + -4y = 7

Reorder the terms:
-4y + y2 = 7

Solving
-4y + y2 = 7

Solving for variable 'y'.

Reorder the terms:
-7 + -4y + y2 = 7 + -7

Combine like terms: 7 + -7 = 0
-7 + -4y + y2 = 0

Begin completing the square.

Move the constant term to the right:

Add '7' to each side of the equation.
-7 + -4y + 7 + y2 = 0 + 7

Reorder the terms:
-7 + 7 + -4y + y2 = 0 + 7

Combine like terms: -7 + 7 = 0
0 + -4y + y2 = 0 + 7
-4y + y2 = 0 + 7

Combine like terms: 0 + 7 = 7
-4y + y2 = 7

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 = 7 + 4

Reorder the terms:
4 + -4y + y2 = 7 + 4

Combine like terms: 7 + 4 = 11
4 + -4y + y2 = 11

Factor a perfect square on the left side:
(y + -2)(y + -2) = 11

Calculate the square root of the right side: 3.31662479

Break this problem into two subproblems by setting 
(y + -2) equal to 3.31662479 and -3.31662479.

Subproblem 1

y + -2 = 3.31662479 Simplifying y + -2 = 3.31662479 Reorder the terms: -2 + y = 3.31662479 Solving -2 + y = 3.31662479 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 = 3.31662479 + 2 Combine like terms: -2 + 2 = 0 0 + y = 3.31662479 + 2 y = 3.31662479 + 2 Combine like terms: 3.31662479 + 2 = 5.31662479 y = 5.31662479 Simplifying y = 5.31662479

Subproblem 2

y + -2 = -3.31662479 Simplifying y + -2 = -3.31662479 Reorder the terms: -2 + y = -3.31662479 Solving -2 + y = -3.31662479 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 = -3.31662479 + 2 Combine like terms: -2 + 2 = 0 0 + y = -3.31662479 + 2 y = -3.31662479 + 2 Combine like terms: -3.31662479 + 2 = -1.31662479 y = -1.31662479 Simplifying y = -1.31662479

Solution

The solution to the problem is based on the solutions from the subproblems. y = {5.31662479, -1.31662479}

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