(x-4)(x+6)=21

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Solution for (x-4)(x+6)=21 equation:


Simplifying
(x + -4)(x + 6) = 21

Reorder the terms:
(-4 + x)(x + 6) = 21

Reorder the terms:
(-4 + x)(6 + x) = 21

Multiply (-4 + x) * (6 + x)
(-4(6 + x) + x(6 + x)) = 21
((6 * -4 + x * -4) + x(6 + x)) = 21
((-24 + -4x) + x(6 + x)) = 21
(-24 + -4x + (6 * x + x * x)) = 21
(-24 + -4x + (6x + x2)) = 21

Combine like terms: -4x + 6x = 2x
(-24 + 2x + x2) = 21

Solving
-24 + 2x + x2 = 21

Solving for variable 'x'.

Reorder the terms:
-24 + -21 + 2x + x2 = 21 + -21

Combine like terms: -24 + -21 = -45
-45 + 2x + x2 = 21 + -21

Combine like terms: 21 + -21 = 0
-45 + 2x + x2 = 0

Begin completing the square.

Move the constant term to the right:

Add '45' to each side of the equation.
-45 + 2x + 45 + x2 = 0 + 45

Reorder the terms:
-45 + 45 + 2x + x2 = 0 + 45

Combine like terms: -45 + 45 = 0
0 + 2x + x2 = 0 + 45
2x + x2 = 0 + 45

Combine like terms: 0 + 45 = 45
2x + x2 = 45

The x term is 2x.  Take half its coefficient (1).
Square it (1) and add it to both sides.

Add '1' to each side of the equation.
2x + 1 + x2 = 45 + 1

Reorder the terms:
1 + 2x + x2 = 45 + 1

Combine like terms: 45 + 1 = 46
1 + 2x + x2 = 46

Factor a perfect square on the left side:
(x + 1)(x + 1) = 46

Calculate the square root of the right side: 6.782329983

Break this problem into two subproblems by setting 
(x + 1) equal to 6.782329983 and -6.782329983.

Subproblem 1

x + 1 = 6.782329983 Simplifying x + 1 = 6.782329983 Reorder the terms: 1 + x = 6.782329983 Solving 1 + x = 6.782329983 Solving for variable 'x'. Move all terms containing x to the left, all other terms to the right. Add '-1' to each side of the equation. 1 + -1 + x = 6.782329983 + -1 Combine like terms: 1 + -1 = 0 0 + x = 6.782329983 + -1 x = 6.782329983 + -1 Combine like terms: 6.782329983 + -1 = 5.782329983 x = 5.782329983 Simplifying x = 5.782329983

Subproblem 2

x + 1 = -6.782329983 Simplifying x + 1 = -6.782329983 Reorder the terms: 1 + x = -6.782329983 Solving 1 + x = -6.782329983 Solving for variable 'x'. Move all terms containing x to the left, all other terms to the right. Add '-1' to each side of the equation. 1 + -1 + x = -6.782329983 + -1 Combine like terms: 1 + -1 = 0 0 + x = -6.782329983 + -1 x = -6.782329983 + -1 Combine like terms: -6.782329983 + -1 = -7.782329983 x = -7.782329983 Simplifying x = -7.782329983

Solution

The solution to the problem is based on the solutions from the subproblems. x = {5.782329983, -7.782329983}

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