5b^2-4b-15=0

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Solution for 5b^2-4b-15=0 equation:


Simplifying
5b2 + -4b + -15 = 0

Reorder the terms:
-15 + -4b + 5b2 = 0

Solving
-15 + -4b + 5b2 = 0

Solving for variable 'b'.

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

Divide each side by '5'.
-3 + -0.8b + b2 = 0

Move the constant term to the right:

Add '3' to each side of the equation.
-3 + -0.8b + 3 + b2 = 0 + 3

Reorder the terms:
-3 + 3 + -0.8b + b2 = 0 + 3

Combine like terms: -3 + 3 = 0
0 + -0.8b + b2 = 0 + 3
-0.8b + b2 = 0 + 3

Combine like terms: 0 + 3 = 3
-0.8b + b2 = 3

The b term is -0.8b.  Take half its coefficient (-0.4).
Square it (0.16) and add it to both sides.

Add '0.16' to each side of the equation.
-0.8b + 0.16 + b2 = 3 + 0.16

Reorder the terms:
0.16 + -0.8b + b2 = 3 + 0.16

Combine like terms: 3 + 0.16 = 3.16
0.16 + -0.8b + b2 = 3.16

Factor a perfect square on the left side:
(b + -0.4)(b + -0.4) = 3.16

Calculate the square root of the right side: 1.777638883

Break this problem into two subproblems by setting 
(b + -0.4) equal to 1.777638883 and -1.777638883.

Subproblem 1

b + -0.4 = 1.777638883 Simplifying b + -0.4 = 1.777638883 Reorder the terms: -0.4 + b = 1.777638883 Solving -0.4 + b = 1.777638883 Solving for variable 'b'. Move all terms containing b to the left, all other terms to the right. Add '0.4' to each side of the equation. -0.4 + 0.4 + b = 1.777638883 + 0.4 Combine like terms: -0.4 + 0.4 = 0.0 0.0 + b = 1.777638883 + 0.4 b = 1.777638883 + 0.4 Combine like terms: 1.777638883 + 0.4 = 2.177638883 b = 2.177638883 Simplifying b = 2.177638883

Subproblem 2

b + -0.4 = -1.777638883 Simplifying b + -0.4 = -1.777638883 Reorder the terms: -0.4 + b = -1.777638883 Solving -0.4 + b = -1.777638883 Solving for variable 'b'. Move all terms containing b to the left, all other terms to the right. Add '0.4' to each side of the equation. -0.4 + 0.4 + b = -1.777638883 + 0.4 Combine like terms: -0.4 + 0.4 = 0.0 0.0 + b = -1.777638883 + 0.4 b = -1.777638883 + 0.4 Combine like terms: -1.777638883 + 0.4 = -1.377638883 b = -1.377638883 Simplifying b = -1.377638883

Solution

The solution to the problem is based on the solutions from the subproblems. b = {2.177638883, -1.377638883}

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