5a^2-10a-21=0

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Solution for 5a^2-10a-21=0 equation:


Simplifying
5a2 + -10a + -21 = 0

Reorder the terms:
-21 + -10a + 5a2 = 0

Solving
-21 + -10a + 5a2 = 0

Solving for variable 'a'.

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

Divide each side by '5'.
-4.2 + -2a + a2 = 0

Move the constant term to the right:

Add '4.2' to each side of the equation.
-4.2 + -2a + 4.2 + a2 = 0 + 4.2

Reorder the terms:
-4.2 + 4.2 + -2a + a2 = 0 + 4.2

Combine like terms: -4.2 + 4.2 = 0.0
0.0 + -2a + a2 = 0 + 4.2
-2a + a2 = 0 + 4.2

Combine like terms: 0 + 4.2 = 4.2
-2a + a2 = 4.2

The a term is -2a.  Take half its coefficient (-1).
Square it (1) and add it to both sides.

Add '1' to each side of the equation.
-2a + 1 + a2 = 4.2 + 1

Reorder the terms:
1 + -2a + a2 = 4.2 + 1

Combine like terms: 4.2 + 1 = 5.2
1 + -2a + a2 = 5.2

Factor a perfect square on the left side:
(a + -1)(a + -1) = 5.2

Calculate the square root of the right side: 2.28035085

Break this problem into two subproblems by setting 
(a + -1) equal to 2.28035085 and -2.28035085.

Subproblem 1

a + -1 = 2.28035085 Simplifying a + -1 = 2.28035085 Reorder the terms: -1 + a = 2.28035085 Solving -1 + a = 2.28035085 Solving for variable 'a'. Move all terms containing a to the left, all other terms to the right. Add '1' to each side of the equation. -1 + 1 + a = 2.28035085 + 1 Combine like terms: -1 + 1 = 0 0 + a = 2.28035085 + 1 a = 2.28035085 + 1 Combine like terms: 2.28035085 + 1 = 3.28035085 a = 3.28035085 Simplifying a = 3.28035085

Subproblem 2

a + -1 = -2.28035085 Simplifying a + -1 = -2.28035085 Reorder the terms: -1 + a = -2.28035085 Solving -1 + a = -2.28035085 Solving for variable 'a'. Move all terms containing a to the left, all other terms to the right. Add '1' to each side of the equation. -1 + 1 + a = -2.28035085 + 1 Combine like terms: -1 + 1 = 0 0 + a = -2.28035085 + 1 a = -2.28035085 + 1 Combine like terms: -2.28035085 + 1 = -1.28035085 a = -1.28035085 Simplifying a = -1.28035085

Solution

The solution to the problem is based on the solutions from the subproblems. a = {3.28035085, -1.28035085}

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