x^2-7x-42=0

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Solution for x^2-7x-42=0 equation:


Simplifying
x2 + -7x + -42 = 0

Reorder the terms:
-42 + -7x + x2 = 0

Solving
-42 + -7x + 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 + -7x + 42 + x2 = 0 + 42

Reorder the terms:
-42 + 42 + -7x + x2 = 0 + 42

Combine like terms: -42 + 42 = 0
0 + -7x + x2 = 0 + 42
-7x + x2 = 0 + 42

Combine like terms: 0 + 42 = 42
-7x + x2 = 42

The x term is -7x.  Take half its coefficient (-3.5).
Square it (12.25) and add it to both sides.

Add '12.25' to each side of the equation.
-7x + 12.25 + x2 = 42 + 12.25

Reorder the terms:
12.25 + -7x + x2 = 42 + 12.25

Combine like terms: 42 + 12.25 = 54.25
12.25 + -7x + x2 = 54.25

Factor a perfect square on the left side:
(x + -3.5)(x + -3.5) = 54.25

Calculate the square root of the right side: 7.365459931

Break this problem into two subproblems by setting 
(x + -3.5) equal to 7.365459931 and -7.365459931.

Subproblem 1

x + -3.5 = 7.365459931 Simplifying x + -3.5 = 7.365459931 Reorder the terms: -3.5 + x = 7.365459931 Solving -3.5 + x = 7.365459931 Solving for variable 'x'. Move all terms containing x to the left, all other terms to the right. Add '3.5' to each side of the equation. -3.5 + 3.5 + x = 7.365459931 + 3.5 Combine like terms: -3.5 + 3.5 = 0.0 0.0 + x = 7.365459931 + 3.5 x = 7.365459931 + 3.5 Combine like terms: 7.365459931 + 3.5 = 10.865459931 x = 10.865459931 Simplifying x = 10.865459931

Subproblem 2

x + -3.5 = -7.365459931 Simplifying x + -3.5 = -7.365459931 Reorder the terms: -3.5 + x = -7.365459931 Solving -3.5 + x = -7.365459931 Solving for variable 'x'. Move all terms containing x to the left, all other terms to the right. Add '3.5' to each side of the equation. -3.5 + 3.5 + x = -7.365459931 + 3.5 Combine like terms: -3.5 + 3.5 = 0.0 0.0 + x = -7.365459931 + 3.5 x = -7.365459931 + 3.5 Combine like terms: -7.365459931 + 3.5 = -3.865459931 x = -3.865459931 Simplifying x = -3.865459931

Solution

The solution to the problem is based on the solutions from the subproblems. x = {10.865459931, -3.865459931}

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