-21-8a=-5a(a+6)

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Solution for -21-8a=-5a(a+6) equation:


Simplifying
-21 + -8a = -5a(a + 6)

Reorder the terms:
-21 + -8a = -5a(6 + a)
-21 + -8a = (6 * -5a + a * -5a)
-21 + -8a = (-30a + -5a2)

Solving
-21 + -8a = -30a + -5a2

Solving for variable 'a'.

Combine like terms: -8a + 30a = 22a
-21 + 22a + 5a2 = -30a + -5a2 + 30a + 5a2

Reorder the terms:
-21 + 22a + 5a2 = -30a + 30a + -5a2 + 5a2

Combine like terms: -30a + 30a = 0
-21 + 22a + 5a2 = 0 + -5a2 + 5a2
-21 + 22a + 5a2 = -5a2 + 5a2

Combine like terms: -5a2 + 5a2 = 0
-21 + 22a + 5a2 = 0

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

Divide each side by '5'.
-4.2 + 4.4a + a2 = 0

Move the constant term to the right:

Add '4.2' to each side of the equation.
-4.2 + 4.4a + 4.2 + a2 = 0 + 4.2

Reorder the terms:
-4.2 + 4.2 + 4.4a + a2 = 0 + 4.2

Combine like terms: -4.2 + 4.2 = 0.0
0.0 + 4.4a + a2 = 0 + 4.2
4.4a + a2 = 0 + 4.2

Combine like terms: 0 + 4.2 = 4.2
4.4a + a2 = 4.2

The a term is 4.4a.  Take half its coefficient (2.2).
Square it (4.84) and add it to both sides.

Add '4.84' to each side of the equation.
4.4a + 4.84 + a2 = 4.2 + 4.84

Reorder the terms:
4.84 + 4.4a + a2 = 4.2 + 4.84

Combine like terms: 4.2 + 4.84 = 9.04
4.84 + 4.4a + a2 = 9.04

Factor a perfect square on the left side:
(a + 2.2)(a + 2.2) = 9.04

Calculate the square root of the right side: 3.006659276

Break this problem into two subproblems by setting 
(a + 2.2) equal to 3.006659276 and -3.006659276.

Subproblem 1

a + 2.2 = 3.006659276 Simplifying a + 2.2 = 3.006659276 Reorder the terms: 2.2 + a = 3.006659276 Solving 2.2 + a = 3.006659276 Solving for variable 'a'. Move all terms containing a to the left, all other terms to the right. Add '-2.2' to each side of the equation. 2.2 + -2.2 + a = 3.006659276 + -2.2 Combine like terms: 2.2 + -2.2 = 0.0 0.0 + a = 3.006659276 + -2.2 a = 3.006659276 + -2.2 Combine like terms: 3.006659276 + -2.2 = 0.806659276 a = 0.806659276 Simplifying a = 0.806659276

Subproblem 2

a + 2.2 = -3.006659276 Simplifying a + 2.2 = -3.006659276 Reorder the terms: 2.2 + a = -3.006659276 Solving 2.2 + a = -3.006659276 Solving for variable 'a'. Move all terms containing a to the left, all other terms to the right. Add '-2.2' to each side of the equation. 2.2 + -2.2 + a = -3.006659276 + -2.2 Combine like terms: 2.2 + -2.2 = 0.0 0.0 + a = -3.006659276 + -2.2 a = -3.006659276 + -2.2 Combine like terms: -3.006659276 + -2.2 = -5.206659276 a = -5.206659276 Simplifying a = -5.206659276

Solution

The solution to the problem is based on the solutions from the subproblems. a = {0.806659276, -5.206659276}

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