x^2+4x-21=25

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Solution for x^2+4x-21=25 equation:


Simplifying
x2 + 4x + -21 = 25

Reorder the terms:
-21 + 4x + x2 = 25

Solving
-21 + 4x + x2 = 25

Solving for variable 'x'.

Reorder the terms:
-21 + -25 + 4x + x2 = 25 + -25

Combine like terms: -21 + -25 = -46
-46 + 4x + x2 = 25 + -25

Combine like terms: 25 + -25 = 0
-46 + 4x + x2 = 0

Begin completing the square.

Move the constant term to the right:

Add '46' to each side of the equation.
-46 + 4x + 46 + x2 = 0 + 46

Reorder the terms:
-46 + 46 + 4x + x2 = 0 + 46

Combine like terms: -46 + 46 = 0
0 + 4x + x2 = 0 + 46
4x + x2 = 0 + 46

Combine like terms: 0 + 46 = 46
4x + x2 = 46

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

Add '4' to each side of the equation.
4x + 4 + x2 = 46 + 4

Reorder the terms:
4 + 4x + x2 = 46 + 4

Combine like terms: 46 + 4 = 50
4 + 4x + x2 = 50

Factor a perfect square on the left side:
(x + 2)(x + 2) = 50

Calculate the square root of the right side: 7.071067812

Break this problem into two subproblems by setting 
(x + 2) equal to 7.071067812 and -7.071067812.

Subproblem 1

x + 2 = 7.071067812 Simplifying x + 2 = 7.071067812 Reorder the terms: 2 + x = 7.071067812 Solving 2 + x = 7.071067812 Solving for variable 'x'. Move all terms containing x to the left, all other terms to the right. Add '-2' to each side of the equation. 2 + -2 + x = 7.071067812 + -2 Combine like terms: 2 + -2 = 0 0 + x = 7.071067812 + -2 x = 7.071067812 + -2 Combine like terms: 7.071067812 + -2 = 5.071067812 x = 5.071067812 Simplifying x = 5.071067812

Subproblem 2

x + 2 = -7.071067812 Simplifying x + 2 = -7.071067812 Reorder the terms: 2 + x = -7.071067812 Solving 2 + x = -7.071067812 Solving for variable 'x'. Move all terms containing x to the left, all other terms to the right. Add '-2' to each side of the equation. 2 + -2 + x = -7.071067812 + -2 Combine like terms: 2 + -2 = 0 0 + x = -7.071067812 + -2 x = -7.071067812 + -2 Combine like terms: -7.071067812 + -2 = -9.071067812 x = -9.071067812 Simplifying x = -9.071067812

Solution

The solution to the problem is based on the solutions from the subproblems. x = {5.071067812, -9.071067812}

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