4x(2x+5)=15

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Solution for 4x(2x+5)=15 equation:


Simplifying
4x(2x + 5) = 15

Reorder the terms:
4x(5 + 2x) = 15
(5 * 4x + 2x * 4x) = 15
(20x + 8x2) = 15

Solving
20x + 8x2 = 15

Solving for variable 'x'.

Reorder the terms:
-15 + 20x + 8x2 = 15 + -15

Combine like terms: 15 + -15 = 0
-15 + 20x + 8x2 = 0

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

Divide each side by '8'.
-1.875 + 2.5x + x2 = 0

Move the constant term to the right:

Add '1.875' to each side of the equation.
-1.875 + 2.5x + 1.875 + x2 = 0 + 1.875

Reorder the terms:
-1.875 + 1.875 + 2.5x + x2 = 0 + 1.875

Combine like terms: -1.875 + 1.875 = 0.000
0.000 + 2.5x + x2 = 0 + 1.875
2.5x + x2 = 0 + 1.875

Combine like terms: 0 + 1.875 = 1.875
2.5x + x2 = 1.875

The x term is 2.5x.  Take half its coefficient (1.25).
Square it (1.5625) and add it to both sides.

Add '1.5625' to each side of the equation.
2.5x + 1.5625 + x2 = 1.875 + 1.5625

Reorder the terms:
1.5625 + 2.5x + x2 = 1.875 + 1.5625

Combine like terms: 1.875 + 1.5625 = 3.4375
1.5625 + 2.5x + x2 = 3.4375

Factor a perfect square on the left side:
(x + 1.25)(x + 1.25) = 3.4375

Calculate the square root of the right side: 1.854049622

Break this problem into two subproblems by setting 
(x + 1.25) equal to 1.854049622 and -1.854049622.

Subproblem 1

x + 1.25 = 1.854049622 Simplifying x + 1.25 = 1.854049622 Reorder the terms: 1.25 + x = 1.854049622 Solving 1.25 + x = 1.854049622 Solving for variable 'x'. Move all terms containing x to the left, all other terms to the right. Add '-1.25' to each side of the equation. 1.25 + -1.25 + x = 1.854049622 + -1.25 Combine like terms: 1.25 + -1.25 = 0.00 0.00 + x = 1.854049622 + -1.25 x = 1.854049622 + -1.25 Combine like terms: 1.854049622 + -1.25 = 0.604049622 x = 0.604049622 Simplifying x = 0.604049622

Subproblem 2

x + 1.25 = -1.854049622 Simplifying x + 1.25 = -1.854049622 Reorder the terms: 1.25 + x = -1.854049622 Solving 1.25 + x = -1.854049622 Solving for variable 'x'. Move all terms containing x to the left, all other terms to the right. Add '-1.25' to each side of the equation. 1.25 + -1.25 + x = -1.854049622 + -1.25 Combine like terms: 1.25 + -1.25 = 0.00 0.00 + x = -1.854049622 + -1.25 x = -1.854049622 + -1.25 Combine like terms: -1.854049622 + -1.25 = -3.104049622 x = -3.104049622 Simplifying x = -3.104049622

Solution

The solution to the problem is based on the solutions from the subproblems. x = {0.604049622, -3.104049622}

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