5x(5x+8)=81

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Solution for 5x(5x+8)=81 equation:


Simplifying
5x(5x + 8) = 81

Reorder the terms:
5x(8 + 5x) = 81
(8 * 5x + 5x * 5x) = 81
(40x + 25x2) = 81

Solving
40x + 25x2 = 81

Solving for variable 'x'.

Reorder the terms:
-81 + 40x + 25x2 = 81 + -81

Combine like terms: 81 + -81 = 0
-81 + 40x + 25x2 = 0

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

Divide each side by '25'.
-3.24 + 1.6x + x2 = 0

Move the constant term to the right:

Add '3.24' to each side of the equation.
-3.24 + 1.6x + 3.24 + x2 = 0 + 3.24

Reorder the terms:
-3.24 + 3.24 + 1.6x + x2 = 0 + 3.24

Combine like terms: -3.24 + 3.24 = 0.00
0.00 + 1.6x + x2 = 0 + 3.24
1.6x + x2 = 0 + 3.24

Combine like terms: 0 + 3.24 = 3.24
1.6x + x2 = 3.24

The x term is 1.6x.  Take half its coefficient (0.8).
Square it (0.64) and add it to both sides.

Add '0.64' to each side of the equation.
1.6x + 0.64 + x2 = 3.24 + 0.64

Reorder the terms:
0.64 + 1.6x + x2 = 3.24 + 0.64

Combine like terms: 3.24 + 0.64 = 3.88
0.64 + 1.6x + x2 = 3.88

Factor a perfect square on the left side:
(x + 0.8)(x + 0.8) = 3.88

Calculate the square root of the right side: 1.96977156

Break this problem into two subproblems by setting 
(x + 0.8) equal to 1.96977156 and -1.96977156.

Subproblem 1

x + 0.8 = 1.96977156 Simplifying x + 0.8 = 1.96977156 Reorder the terms: 0.8 + x = 1.96977156 Solving 0.8 + x = 1.96977156 Solving for variable 'x'. Move all terms containing x to the left, all other terms to the right. Add '-0.8' to each side of the equation. 0.8 + -0.8 + x = 1.96977156 + -0.8 Combine like terms: 0.8 + -0.8 = 0.0 0.0 + x = 1.96977156 + -0.8 x = 1.96977156 + -0.8 Combine like terms: 1.96977156 + -0.8 = 1.16977156 x = 1.16977156 Simplifying x = 1.16977156

Subproblem 2

x + 0.8 = -1.96977156 Simplifying x + 0.8 = -1.96977156 Reorder the terms: 0.8 + x = -1.96977156 Solving 0.8 + x = -1.96977156 Solving for variable 'x'. Move all terms containing x to the left, all other terms to the right. Add '-0.8' to each side of the equation. 0.8 + -0.8 + x = -1.96977156 + -0.8 Combine like terms: 0.8 + -0.8 = 0.0 0.0 + x = -1.96977156 + -0.8 x = -1.96977156 + -0.8 Combine like terms: -1.96977156 + -0.8 = -2.76977156 x = -2.76977156 Simplifying x = -2.76977156

Solution

The solution to the problem is based on the solutions from the subproblems. x = {1.16977156, -2.76977156}

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