x^2+21x-42=0

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Solution for x^2+21x-42=0 equation:


Simplifying
x2 + 21x + -42 = 0

Reorder the terms:
-42 + 21x + x2 = 0

Solving
-42 + 21x + x2 = 0

Solving for variable 'x'.

Begin completing the square.

Move the constant term to the right:

Add '42' to each side of the equation.
-42 + 21x + 42 + x2 = 0 + 42

Reorder the terms:
-42 + 42 + 21x + x2 = 0 + 42

Combine like terms: -42 + 42 = 0
0 + 21x + x2 = 0 + 42
21x + x2 = 0 + 42

Combine like terms: 0 + 42 = 42
21x + x2 = 42

The x term is 21x.  Take half its coefficient (10.5).
Square it (110.25) and add it to both sides.

Add '110.25' to each side of the equation.
21x + 110.25 + x2 = 42 + 110.25

Reorder the terms:
110.25 + 21x + x2 = 42 + 110.25

Combine like terms: 42 + 110.25 = 152.25
110.25 + 21x + x2 = 152.25

Factor a perfect square on the left side:
(x + 10.5)(x + 10.5) = 152.25

Calculate the square root of the right side: 12.338962679

Break this problem into two subproblems by setting 
(x + 10.5) equal to 12.338962679 and -12.338962679.

Subproblem 1

x + 10.5 = 12.338962679 Simplifying x + 10.5 = 12.338962679 Reorder the terms: 10.5 + x = 12.338962679 Solving 10.5 + x = 12.338962679 Solving for variable 'x'. Move all terms containing x to the left, all other terms to the right. Add '-10.5' to each side of the equation. 10.5 + -10.5 + x = 12.338962679 + -10.5 Combine like terms: 10.5 + -10.5 = 0.0 0.0 + x = 12.338962679 + -10.5 x = 12.338962679 + -10.5 Combine like terms: 12.338962679 + -10.5 = 1.838962679 x = 1.838962679 Simplifying x = 1.838962679

Subproblem 2

x + 10.5 = -12.338962679 Simplifying x + 10.5 = -12.338962679 Reorder the terms: 10.5 + x = -12.338962679 Solving 10.5 + x = -12.338962679 Solving for variable 'x'. Move all terms containing x to the left, all other terms to the right. Add '-10.5' to each side of the equation. 10.5 + -10.5 + x = -12.338962679 + -10.5 Combine like terms: 10.5 + -10.5 = 0.0 0.0 + x = -12.338962679 + -10.5 x = -12.338962679 + -10.5 Combine like terms: -12.338962679 + -10.5 = -22.838962679 x = -22.838962679 Simplifying x = -22.838962679

Solution

The solution to the problem is based on the solutions from the subproblems. x = {1.838962679, -22.838962679}

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