c^2-4c-21=0

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Solution for c^2-4c-21=0 equation: 


Simplifying
c2 + -4c + -21 = 0

Reorder the terms:
-21 + -4c + c2 = 0

Solving
-21 + -4c + c2 = 0

Solving for variable 'c'.

Factor a trinomial.
(-3 + -1c)(7 + -1c) = 0


Subproblem 1
Set the factor '(-3 + -1c)' equal to zero and attempt to solve:

Simplifying
-3 + -1c = 0

Solving
-3 + -1c = 0

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

Add '3' to each side of the equation.
-3 + 3 + -1c = 0 + 3

Combine like terms: -3 + 3 = 0
0 + -1c = 0 + 3
-1c = 0 + 3

Combine like terms: 0 + 3 = 3
-1c = 3

Divide each side by '-1'.
c = -3

Simplifying
c = -3

Subproblem 2
Set the factor '(7 + -1c)' equal to zero and attempt to solve:

Simplifying
7 + -1c = 0

Solving
7 + -1c = 0

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

Add '-7' to each side of the equation.
7 + -7 + -1c = 0 + -7

Combine like terms: 7 + -7 = 0
0 + -1c = 0 + -7
-1c = 0 + -7

Combine like terms: 0 + -7 = -7
-1c = -7

Divide each side by '-1'.
c = 7

Simplifying
c = 7
Solution
c = {-3, 7}

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