4k^2+21k-20=0

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Solution for 4k^2+21k-20=0 equation:


Simplifying
4k2 + 21k + -20 = 0

Reorder the terms:
-20 + 21k + 4k2 = 0

Solving
-20 + 21k + 4k2 = 0

Solving for variable 'k'.

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

Divide each side by '4'.
-5 + 5.25k + k2 = 0

Move the constant term to the right:

Add '5' to each side of the equation.
-5 + 5.25k + 5 + k2 = 0 + 5

Reorder the terms:
-5 + 5 + 5.25k + k2 = 0 + 5

Combine like terms: -5 + 5 = 0
0 + 5.25k + k2 = 0 + 5
5.25k + k2 = 0 + 5

Combine like terms: 0 + 5 = 5
5.25k + k2 = 5

The k term is 5.25k.  Take half its coefficient (2.625).
Square it (6.890625) and add it to both sides.

Add '6.890625' to each side of the equation.
5.25k + 6.890625 + k2 = 5 + 6.890625

Reorder the terms:
6.890625 + 5.25k + k2 = 5 + 6.890625

Combine like terms: 5 + 6.890625 = 11.890625
6.890625 + 5.25k + k2 = 11.890625

Factor a perfect square on the left side:
(k + 2.625)(k + 2.625) = 11.890625

Calculate the square root of the right side: 3.448278556

Break this problem into two subproblems by setting 
(k + 2.625) equal to 3.448278556 and -3.448278556.

Subproblem 1

k + 2.625 = 3.448278556 Simplifying k + 2.625 = 3.448278556 Reorder the terms: 2.625 + k = 3.448278556 Solving 2.625 + k = 3.448278556 Solving for variable 'k'. Move all terms containing k to the left, all other terms to the right. Add '-2.625' to each side of the equation. 2.625 + -2.625 + k = 3.448278556 + -2.625 Combine like terms: 2.625 + -2.625 = 0.000 0.000 + k = 3.448278556 + -2.625 k = 3.448278556 + -2.625 Combine like terms: 3.448278556 + -2.625 = 0.823278556 k = 0.823278556 Simplifying k = 0.823278556

Subproblem 2

k + 2.625 = -3.448278556 Simplifying k + 2.625 = -3.448278556 Reorder the terms: 2.625 + k = -3.448278556 Solving 2.625 + k = -3.448278556 Solving for variable 'k'. Move all terms containing k to the left, all other terms to the right. Add '-2.625' to each side of the equation. 2.625 + -2.625 + k = -3.448278556 + -2.625 Combine like terms: 2.625 + -2.625 = 0.000 0.000 + k = -3.448278556 + -2.625 k = -3.448278556 + -2.625 Combine like terms: -3.448278556 + -2.625 = -6.073278556 k = -6.073278556 Simplifying k = -6.073278556

Solution

The solution to the problem is based on the solutions from the subproblems. k = {0.823278556, -6.073278556}

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