3c^2+7c-42=0

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Solution for 3c^2+7c-42=0 equation:


Simplifying
3c2 + 7c + -42 = 0

Reorder the terms:
-42 + 7c + 3c2 = 0

Solving
-42 + 7c + 3c2 = 0

Solving for variable 'c'.

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

Divide each side by '3'.
-14 + 2.333333333c + c2 = 0

Move the constant term to the right:

Add '14' to each side of the equation.
-14 + 2.333333333c + 14 + c2 = 0 + 14

Reorder the terms:
-14 + 14 + 2.333333333c + c2 = 0 + 14

Combine like terms: -14 + 14 = 0
0 + 2.333333333c + c2 = 0 + 14
2.333333333c + c2 = 0 + 14

Combine like terms: 0 + 14 = 14
2.333333333c + c2 = 14

The c term is 2.333333333c.  Take half its coefficient (1.166666667).
Square it (1.361111112) and add it to both sides.

Add '1.361111112' to each side of the equation.
2.333333333c + 1.361111112 + c2 = 14 + 1.361111112

Reorder the terms:
1.361111112 + 2.333333333c + c2 = 14 + 1.361111112

Combine like terms: 14 + 1.361111112 = 15.361111112
1.361111112 + 2.333333333c + c2 = 15.361111112

Factor a perfect square on the left side:
(c + 1.166666667)(c + 1.166666667) = 15.361111112

Calculate the square root of the right side: 3.919325339

Break this problem into two subproblems by setting 
(c + 1.166666667) equal to 3.919325339 and -3.919325339.

Subproblem 1

c + 1.166666667 = 3.919325339 Simplifying c + 1.166666667 = 3.919325339 Reorder the terms: 1.166666667 + c = 3.919325339 Solving 1.166666667 + c = 3.919325339 Solving for variable 'c'. Move all terms containing c to the left, all other terms to the right. Add '-1.166666667' to each side of the equation. 1.166666667 + -1.166666667 + c = 3.919325339 + -1.166666667 Combine like terms: 1.166666667 + -1.166666667 = 0.000000000 0.000000000 + c = 3.919325339 + -1.166666667 c = 3.919325339 + -1.166666667 Combine like terms: 3.919325339 + -1.166666667 = 2.752658672 c = 2.752658672 Simplifying c = 2.752658672

Subproblem 2

c + 1.166666667 = -3.919325339 Simplifying c + 1.166666667 = -3.919325339 Reorder the terms: 1.166666667 + c = -3.919325339 Solving 1.166666667 + c = -3.919325339 Solving for variable 'c'. Move all terms containing c to the left, all other terms to the right. Add '-1.166666667' to each side of the equation. 1.166666667 + -1.166666667 + c = -3.919325339 + -1.166666667 Combine like terms: 1.166666667 + -1.166666667 = 0.000000000 0.000000000 + c = -3.919325339 + -1.166666667 c = -3.919325339 + -1.166666667 Combine like terms: -3.919325339 + -1.166666667 = -5.085992006 c = -5.085992006 Simplifying c = -5.085992006

Solution

The solution to the problem is based on the solutions from the subproblems. c = {2.752658672, -5.085992006}

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