42=20*x+4.9*x^2

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Solution for 42=20*x+4.9*x^2 equation:


Simplifying
42 = 20x + 4.9x2

Solving
42 = 20x + 4.9x2

Solving for variable 'x'.

Reorder the terms:
42 + -20x + -4.9x2 = 20x + -20x + 4.9x2 + -4.9x2

Combine like terms: 20x + -20x = 0
42 + -20x + -4.9x2 = 0 + 4.9x2 + -4.9x2
42 + -20x + -4.9x2 = 4.9x2 + -4.9x2

Combine like terms: 4.9x2 + -4.9x2 = 0.0
42 + -20x + -4.9x2 = 0.0

Begin completing the square.  Divide all terms by
-4.9 the coefficient of the squared term: 

Divide each side by '-4.9'.
-8.571428571 + 4.081632653x + x2 = 0

Move the constant term to the right:

Add '8.571428571' to each side of the equation.
-8.571428571 + 4.081632653x + 8.571428571 + x2 = 0 + 8.571428571

Reorder the terms:
-8.571428571 + 8.571428571 + 4.081632653x + x2 = 0 + 8.571428571

Combine like terms: -8.571428571 + 8.571428571 = 0.000000000
0.000000000 + 4.081632653x + x2 = 0 + 8.571428571
4.081632653x + x2 = 0 + 8.571428571

Combine like terms: 0 + 8.571428571 = 8.571428571
4.081632653x + x2 = 8.571428571

The x term is 4.081632653x.  Take half its coefficient (2.040816327).
Square it (4.164931281) and add it to both sides.

Add '4.164931281' to each side of the equation.
4.081632653x + 4.164931281 + x2 = 8.571428571 + 4.164931281

Reorder the terms:
4.164931281 + 4.081632653x + x2 = 8.571428571 + 4.164931281

Combine like terms: 8.571428571 + 4.164931281 = 12.736359852
4.164931281 + 4.081632653x + x2 = 12.736359852

Factor a perfect square on the left side:
(x + 2.040816327)(x + 2.040816327) = 12.736359852

Calculate the square root of the right side: 3.5688037

Break this problem into two subproblems by setting 
(x + 2.040816327) equal to 3.5688037 and -3.5688037.

Subproblem 1

x + 2.040816327 = 3.5688037 Simplifying x + 2.040816327 = 3.5688037 Reorder the terms: 2.040816327 + x = 3.5688037 Solving 2.040816327 + x = 3.5688037 Solving for variable 'x'. Move all terms containing x to the left, all other terms to the right. Add '-2.040816327' to each side of the equation. 2.040816327 + -2.040816327 + x = 3.5688037 + -2.040816327 Combine like terms: 2.040816327 + -2.040816327 = 0.000000000 0.000000000 + x = 3.5688037 + -2.040816327 x = 3.5688037 + -2.040816327 Combine like terms: 3.5688037 + -2.040816327 = 1.527987373 x = 1.527987373 Simplifying x = 1.527987373

Subproblem 2

x + 2.040816327 = -3.5688037 Simplifying x + 2.040816327 = -3.5688037 Reorder the terms: 2.040816327 + x = -3.5688037 Solving 2.040816327 + x = -3.5688037 Solving for variable 'x'. Move all terms containing x to the left, all other terms to the right. Add '-2.040816327' to each side of the equation. 2.040816327 + -2.040816327 + x = -3.5688037 + -2.040816327 Combine like terms: 2.040816327 + -2.040816327 = 0.000000000 0.000000000 + x = -3.5688037 + -2.040816327 x = -3.5688037 + -2.040816327 Combine like terms: -3.5688037 + -2.040816327 = -5.609620027 x = -5.609620027 Simplifying x = -5.609620027

Solution

The solution to the problem is based on the solutions from the subproblems. x = {1.527987373, -5.609620027}

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