2X^2+20X=-21

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Solution for 2X^2+20X=-21 equation:


Simplifying
2X2 + 20X = -21

Reorder the terms:
20X + 2X2 = -21

Solving
20X + 2X2 = -21

Solving for variable 'X'.

Reorder the terms:
21 + 20X + 2X2 = -21 + 21

Combine like terms: -21 + 21 = 0
21 + 20X + 2X2 = 0

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

Divide each side by '2'.
10.5 + 10X + X2 = 0

Move the constant term to the right:

Add '-10.5' to each side of the equation.
10.5 + 10X + -10.5 + X2 = 0 + -10.5

Reorder the terms:
10.5 + -10.5 + 10X + X2 = 0 + -10.5

Combine like terms: 10.5 + -10.5 = 0.0
0.0 + 10X + X2 = 0 + -10.5
10X + X2 = 0 + -10.5

Combine like terms: 0 + -10.5 = -10.5
10X + X2 = -10.5

The X term is 10X.  Take half its coefficient (5).
Square it (25) and add it to both sides.

Add '25' to each side of the equation.
10X + 25 + X2 = -10.5 + 25

Reorder the terms:
25 + 10X + X2 = -10.5 + 25

Combine like terms: -10.5 + 25 = 14.5
25 + 10X + X2 = 14.5

Factor a perfect square on the left side:
(X + 5)(X + 5) = 14.5

Calculate the square root of the right side: 3.807886553

Break this problem into two subproblems by setting 
(X + 5) equal to 3.807886553 and -3.807886553.

Subproblem 1

X + 5 = 3.807886553 Simplifying X + 5 = 3.807886553 Reorder the terms: 5 + X = 3.807886553 Solving 5 + X = 3.807886553 Solving for variable 'X'. Move all terms containing X to the left, all other terms to the right. Add '-5' to each side of the equation. 5 + -5 + X = 3.807886553 + -5 Combine like terms: 5 + -5 = 0 0 + X = 3.807886553 + -5 X = 3.807886553 + -5 Combine like terms: 3.807886553 + -5 = -1.192113447 X = -1.192113447 Simplifying X = -1.192113447

Subproblem 2

X + 5 = -3.807886553 Simplifying X + 5 = -3.807886553 Reorder the terms: 5 + X = -3.807886553 Solving 5 + X = -3.807886553 Solving for variable 'X'. Move all terms containing X to the left, all other terms to the right. Add '-5' to each side of the equation. 5 + -5 + X = -3.807886553 + -5 Combine like terms: 5 + -5 = 0 0 + X = -3.807886553 + -5 X = -3.807886553 + -5 Combine like terms: -3.807886553 + -5 = -8.807886553 X = -8.807886553 Simplifying X = -8.807886553

Solution

The solution to the problem is based on the solutions from the subproblems. X = {-1.192113447, -8.807886553}

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