4x^2+5x=80

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Solution for 4x^2+5x=80 equation:


Simplifying
4x2 + 5x = 80

Reorder the terms:
5x + 4x2 = 80

Solving
5x + 4x2 = 80

Solving for variable 'x'.

Reorder the terms:
-80 + 5x + 4x2 = 80 + -80

Combine like terms: 80 + -80 = 0
-80 + 5x + 4x2 = 0

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

Divide each side by '4'.
-20 + 1.25x + x2 = 0

Move the constant term to the right:

Add '20' to each side of the equation.
-20 + 1.25x + 20 + x2 = 0 + 20

Reorder the terms:
-20 + 20 + 1.25x + x2 = 0 + 20

Combine like terms: -20 + 20 = 0
0 + 1.25x + x2 = 0 + 20
1.25x + x2 = 0 + 20

Combine like terms: 0 + 20 = 20
1.25x + x2 = 20

The x term is 1.25x.  Take half its coefficient (0.625).
Square it (0.390625) and add it to both sides.

Add '0.390625' to each side of the equation.
1.25x + 0.390625 + x2 = 20 + 0.390625

Reorder the terms:
0.390625 + 1.25x + x2 = 20 + 0.390625

Combine like terms: 20 + 0.390625 = 20.390625
0.390625 + 1.25x + x2 = 20.390625

Factor a perfect square on the left side:
(x + 0.625)(x + 0.625) = 20.390625

Calculate the square root of the right side: 4.515597967

Break this problem into two subproblems by setting 
(x + 0.625) equal to 4.515597967 and -4.515597967.

Subproblem 1

x + 0.625 = 4.515597967 Simplifying x + 0.625 = 4.515597967 Reorder the terms: 0.625 + x = 4.515597967 Solving 0.625 + x = 4.515597967 Solving for variable 'x'. Move all terms containing x to the left, all other terms to the right. Add '-0.625' to each side of the equation. 0.625 + -0.625 + x = 4.515597967 + -0.625 Combine like terms: 0.625 + -0.625 = 0.000 0.000 + x = 4.515597967 + -0.625 x = 4.515597967 + -0.625 Combine like terms: 4.515597967 + -0.625 = 3.890597967 x = 3.890597967 Simplifying x = 3.890597967

Subproblem 2

x + 0.625 = -4.515597967 Simplifying x + 0.625 = -4.515597967 Reorder the terms: 0.625 + x = -4.515597967 Solving 0.625 + x = -4.515597967 Solving for variable 'x'. Move all terms containing x to the left, all other terms to the right. Add '-0.625' to each side of the equation. 0.625 + -0.625 + x = -4.515597967 + -0.625 Combine like terms: 0.625 + -0.625 = 0.000 0.000 + x = -4.515597967 + -0.625 x = -4.515597967 + -0.625 Combine like terms: -4.515597967 + -0.625 = -5.140597967 x = -5.140597967 Simplifying x = -5.140597967

Solution

The solution to the problem is based on the solutions from the subproblems. x = {3.890597967, -5.140597967}

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