-2c(-c-20)=-2c-20

Solution for -2c(-c-20)=-2c-20 equation:

Simplifying
-2c(-1c + -20) = -2c + -20

Reorder the terms:
-2c(-20 + -1c) = -2c + -20
(-20 * -2c + -1c * -2c) = -2c + -20
(40c + 2c2) = -2c + -20

Reorder the terms:
40c + 2c2 = -20 + -2c

Solving
40c + 2c2 = -20 + -2c

Solving for variable 'c'.

Reorder the terms:
20 + 40c + 2c + 2c2 = -20 + -2c + 20 + 2c

Combine like terms: 40c + 2c = 42c
20 + 42c + 2c2 = -20 + -2c + 20 + 2c

Reorder the terms:
20 + 42c + 2c2 = -20 + 20 + -2c + 2c

Combine like terms: -20 + 20 = 0
20 + 42c + 2c2 = 0 + -2c + 2c
20 + 42c + 2c2 = -2c + 2c

Combine like terms: -2c + 2c = 0
20 + 42c + 2c2 = 0

Factor out the Greatest Common Factor (GCF), '2'.
2(10 + 21c + c2) = 0

Ignore the factor 2.
Subproblem 1
Set the factor '(10 + 21c + c2)' equal to zero and attempt to solve:

Simplifying
10 + 21c + c2 = 0

Solving
10 + 21c + c2 = 0

Begin completing the square.

Move the constant term to the right:

Add '-10' to each side of the equation.
10 + 21c + -10 + c2 = 0 + -10

Reorder the terms:
10 + -10 + 21c + c2 = 0 + -10

Combine like terms: 10 + -10 = 0
0 + 21c + c2 = 0 + -10
21c + c2 = 0 + -10

Combine like terms: 0 + -10 = -10
21c + c2 = -10

The c term is 21c.  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.
21c + 110.25 + c2 = -10 + 110.25

Reorder the terms:
110.25 + 21c + c2 = -10 + 110.25

Combine like terms: -10 + 110.25 = 100.25
110.25 + 21c + c2 = 100.25

Factor a perfect square on the left side:
(c + 10.5)(c + 10.5) = 100.25

Calculate the square root of the right side: 10.012492197

Break this problem into two subproblems by setting 
(c + 10.5) equal to 10.012492197 and -10.012492197.

Subproblem 1
c + 10.5 = 10.012492197

Simplifying
c + 10.5 = 10.012492197

Reorder the terms:
10.5 + c = 10.012492197

Solving
10.5 + c = 10.012492197

Solving for variable 'c'.

Move all terms containing c to the left, all other terms to the right.

Add '-10.5' to each side of the equation.
10.5 + -10.5 + c = 10.012492197 + -10.5

Combine like terms: 10.5 + -10.5 = 0.0
0.0 + c = 10.012492197 + -10.5
c = 10.012492197 + -10.5

Combine like terms: 10.012492197 + -10.5 = -0.487507803
c = -0.487507803

Simplifying
c = -0.487507803

Subproblem 2
c + 10.5 = -10.012492197

Simplifying
c + 10.5 = -10.012492197

Reorder the terms:
10.5 + c = -10.012492197

Solving
10.5 + c = -10.012492197

Solving for variable 'c'.

Move all terms containing c to the left, all other terms to the right.

Add '-10.5' to each side of the equation.
10.5 + -10.5 + c = -10.012492197 + -10.5

Combine like terms: 10.5 + -10.5 = 0.0
0.0 + c = -10.012492197 + -10.5
c = -10.012492197 + -10.5

Combine like terms: -10.012492197 + -10.5 = -20.512492197
c = -20.512492197

Simplifying
c = -20.512492197

Solution
The solution to the problem is based on the solutions
from the subproblems.
c = {-0.487507803, -20.512492197}
Solution
c = {-0.487507803, -20.512492197}