5x^2-6x-21=0

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Solution for 5x^2-6x-21=0 equation:


Simplifying
5x2 + -6x + -21 = 0

Reorder the terms:
-21 + -6x + 5x2 = 0

Solving
-21 + -6x + 5x2 = 0

Solving for variable 'x'.

Begin completing the square.  Divide all terms by
5 the coefficient of the squared term: 

Divide each side by '5'.
-4.2 + -1.2x + x2 = 0

Move the constant term to the right:

Add '4.2' to each side of the equation.
-4.2 + -1.2x + 4.2 + x2 = 0 + 4.2

Reorder the terms:
-4.2 + 4.2 + -1.2x + x2 = 0 + 4.2

Combine like terms: -4.2 + 4.2 = 0.0
0.0 + -1.2x + x2 = 0 + 4.2
-1.2x + x2 = 0 + 4.2

Combine like terms: 0 + 4.2 = 4.2
-1.2x + x2 = 4.2

The x term is -1.2x.  Take half its coefficient (-0.6).
Square it (0.36) and add it to both sides.

Add '0.36' to each side of the equation.
-1.2x + 0.36 + x2 = 4.2 + 0.36

Reorder the terms:
0.36 + -1.2x + x2 = 4.2 + 0.36

Combine like terms: 4.2 + 0.36 = 4.56
0.36 + -1.2x + x2 = 4.56

Factor a perfect square on the left side:
(x + -0.6)(x + -0.6) = 4.56

Calculate the square root of the right side: 2.13541565

Break this problem into two subproblems by setting 
(x + -0.6) equal to 2.13541565 and -2.13541565.

Subproblem 1

x + -0.6 = 2.13541565 Simplifying x + -0.6 = 2.13541565 Reorder the terms: -0.6 + x = 2.13541565 Solving -0.6 + x = 2.13541565 Solving for variable 'x'. Move all terms containing x to the left, all other terms to the right. Add '0.6' to each side of the equation. -0.6 + 0.6 + x = 2.13541565 + 0.6 Combine like terms: -0.6 + 0.6 = 0.0 0.0 + x = 2.13541565 + 0.6 x = 2.13541565 + 0.6 Combine like terms: 2.13541565 + 0.6 = 2.73541565 x = 2.73541565 Simplifying x = 2.73541565

Subproblem 2

x + -0.6 = -2.13541565 Simplifying x + -0.6 = -2.13541565 Reorder the terms: -0.6 + x = -2.13541565 Solving -0.6 + x = -2.13541565 Solving for variable 'x'. Move all terms containing x to the left, all other terms to the right. Add '0.6' to each side of the equation. -0.6 + 0.6 + x = -2.13541565 + 0.6 Combine like terms: -0.6 + 0.6 = 0.0 0.0 + x = -2.13541565 + 0.6 x = -2.13541565 + 0.6 Combine like terms: -2.13541565 + 0.6 = -1.53541565 x = -1.53541565 Simplifying x = -1.53541565

Solution

The solution to the problem is based on the solutions from the subproblems. x = {2.73541565, -1.53541565}

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