d^2-20d=-21

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Solution for d^2-20d=-21 equation:


Simplifying
d2 + -20d = -21

Reorder the terms:
-20d + d2 = -21

Solving
-20d + d2 = -21

Solving for variable 'd'.

Reorder the terms:
21 + -20d + d2 = -21 + 21

Combine like terms: -21 + 21 = 0
21 + -20d + d2 = 0

Begin completing the square.

Move the constant term to the right:

Add '-21' to each side of the equation.
21 + -20d + -21 + d2 = 0 + -21

Reorder the terms:
21 + -21 + -20d + d2 = 0 + -21

Combine like terms: 21 + -21 = 0
0 + -20d + d2 = 0 + -21
-20d + d2 = 0 + -21

Combine like terms: 0 + -21 = -21
-20d + d2 = -21

The d term is -20d.  Take half its coefficient (-10).
Square it (100) and add it to both sides.

Add '100' to each side of the equation.
-20d + 100 + d2 = -21 + 100

Reorder the terms:
100 + -20d + d2 = -21 + 100

Combine like terms: -21 + 100 = 79
100 + -20d + d2 = 79

Factor a perfect square on the left side:
(d + -10)(d + -10) = 79

Calculate the square root of the right side: 8.888194417

Break this problem into two subproblems by setting 
(d + -10) equal to 8.888194417 and -8.888194417.

Subproblem 1

d + -10 = 8.888194417 Simplifying d + -10 = 8.888194417 Reorder the terms: -10 + d = 8.888194417 Solving -10 + d = 8.888194417 Solving for variable 'd'. Move all terms containing d to the left, all other terms to the right. Add '10' to each side of the equation. -10 + 10 + d = 8.888194417 + 10 Combine like terms: -10 + 10 = 0 0 + d = 8.888194417 + 10 d = 8.888194417 + 10 Combine like terms: 8.888194417 + 10 = 18.888194417 d = 18.888194417 Simplifying d = 18.888194417

Subproblem 2

d + -10 = -8.888194417 Simplifying d + -10 = -8.888194417 Reorder the terms: -10 + d = -8.888194417 Solving -10 + d = -8.888194417 Solving for variable 'd'. Move all terms containing d to the left, all other terms to the right. Add '10' to each side of the equation. -10 + 10 + d = -8.888194417 + 10 Combine like terms: -10 + 10 = 0 0 + d = -8.888194417 + 10 d = -8.888194417 + 10 Combine like terms: -8.888194417 + 10 = 1.111805583 d = 1.111805583 Simplifying d = 1.111805583

Solution

The solution to the problem is based on the solutions from the subproblems. d = {18.888194417, 1.111805583}

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