4x^2+15x-40=0

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Solution for 4x^2+15x-40=0 equation:


Simplifying
4x2 + 15x + -40 = 0

Reorder the terms:
-40 + 15x + 4x2 = 0

Solving
-40 + 15x + 4x2 = 0

Solving for variable 'x'.

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

Divide each side by '4'.
-10 + 3.75x + x2 = 0

Move the constant term to the right:

Add '10' to each side of the equation.
-10 + 3.75x + 10 + x2 = 0 + 10

Reorder the terms:
-10 + 10 + 3.75x + x2 = 0 + 10

Combine like terms: -10 + 10 = 0
0 + 3.75x + x2 = 0 + 10
3.75x + x2 = 0 + 10

Combine like terms: 0 + 10 = 10
3.75x + x2 = 10

The x term is 3.75x.  Take half its coefficient (1.875).
Square it (3.515625) and add it to both sides.

Add '3.515625' to each side of the equation.
3.75x + 3.515625 + x2 = 10 + 3.515625

Reorder the terms:
3.515625 + 3.75x + x2 = 10 + 3.515625

Combine like terms: 10 + 3.515625 = 13.515625
3.515625 + 3.75x + x2 = 13.515625

Factor a perfect square on the left side:
(x + 1.875)(x + 1.875) = 13.515625

Calculate the square root of the right side: 3.676360292

Break this problem into two subproblems by setting 
(x + 1.875) equal to 3.676360292 and -3.676360292.

Subproblem 1

x + 1.875 = 3.676360292 Simplifying x + 1.875 = 3.676360292 Reorder the terms: 1.875 + x = 3.676360292 Solving 1.875 + x = 3.676360292 Solving for variable 'x'. Move all terms containing x to the left, all other terms to the right. Add '-1.875' to each side of the equation. 1.875 + -1.875 + x = 3.676360292 + -1.875 Combine like terms: 1.875 + -1.875 = 0.000 0.000 + x = 3.676360292 + -1.875 x = 3.676360292 + -1.875 Combine like terms: 3.676360292 + -1.875 = 1.801360292 x = 1.801360292 Simplifying x = 1.801360292

Subproblem 2

x + 1.875 = -3.676360292 Simplifying x + 1.875 = -3.676360292 Reorder the terms: 1.875 + x = -3.676360292 Solving 1.875 + x = -3.676360292 Solving for variable 'x'. Move all terms containing x to the left, all other terms to the right. Add '-1.875' to each side of the equation. 1.875 + -1.875 + x = -3.676360292 + -1.875 Combine like terms: 1.875 + -1.875 = 0.000 0.000 + x = -3.676360292 + -1.875 x = -3.676360292 + -1.875 Combine like terms: -3.676360292 + -1.875 = -5.551360292 x = -5.551360292 Simplifying x = -5.551360292

Solution

The solution to the problem is based on the solutions from the subproblems. x = {1.801360292, -5.551360292}

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