x^2+8x-21=3

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Solution for x^2+8x-21=3 equation:


Simplifying
x2 + 8x + -21 = 3

Reorder the terms:
-21 + 8x + x2 = 3

Solving
-21 + 8x + x2 = 3

Solving for variable 'x'.

Reorder the terms:
-21 + -3 + 8x + x2 = 3 + -3

Combine like terms: -21 + -3 = -24
-24 + 8x + x2 = 3 + -3

Combine like terms: 3 + -3 = 0
-24 + 8x + x2 = 0

Begin completing the square.

Move the constant term to the right:

Add '24' to each side of the equation.
-24 + 8x + 24 + x2 = 0 + 24

Reorder the terms:
-24 + 24 + 8x + x2 = 0 + 24

Combine like terms: -24 + 24 = 0
0 + 8x + x2 = 0 + 24
8x + x2 = 0 + 24

Combine like terms: 0 + 24 = 24
8x + x2 = 24

The x term is 8x.  Take half its coefficient (4).
Square it (16) and add it to both sides.

Add '16' to each side of the equation.
8x + 16 + x2 = 24 + 16

Reorder the terms:
16 + 8x + x2 = 24 + 16

Combine like terms: 24 + 16 = 40
16 + 8x + x2 = 40

Factor a perfect square on the left side:
(x + 4)(x + 4) = 40

Calculate the square root of the right side: 6.32455532

Break this problem into two subproblems by setting 
(x + 4) equal to 6.32455532 and -6.32455532.

Subproblem 1

x + 4 = 6.32455532 Simplifying x + 4 = 6.32455532 Reorder the terms: 4 + x = 6.32455532 Solving 4 + x = 6.32455532 Solving for variable 'x'. Move all terms containing x to the left, all other terms to the right. Add '-4' to each side of the equation. 4 + -4 + x = 6.32455532 + -4 Combine like terms: 4 + -4 = 0 0 + x = 6.32455532 + -4 x = 6.32455532 + -4 Combine like terms: 6.32455532 + -4 = 2.32455532 x = 2.32455532 Simplifying x = 2.32455532

Subproblem 2

x + 4 = -6.32455532 Simplifying x + 4 = -6.32455532 Reorder the terms: 4 + x = -6.32455532 Solving 4 + x = -6.32455532 Solving for variable 'x'. Move all terms containing x to the left, all other terms to the right. Add '-4' to each side of the equation. 4 + -4 + x = -6.32455532 + -4 Combine like terms: 4 + -4 = 0 0 + x = -6.32455532 + -4 x = -6.32455532 + -4 Combine like terms: -6.32455532 + -4 = -10.32455532 x = -10.32455532 Simplifying x = -10.32455532

Solution

The solution to the problem is based on the solutions from the subproblems. x = {2.32455532, -10.32455532}

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