20=42*x-4.9x^2

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


Simplifying
20 = 42x + -4.9x2

Solving
20 = 42x + -4.9x2

Solving for variable 'x'.

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

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

Combine like terms: -4.9x2 + 4.9x2 = 0.0
20 + -42x + 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'.
4.081632653 + -8.571428571x + x2 = 0

Move the constant term to the right:

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

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

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

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

The x term is -8.571428571x.  Take half its coefficient (-4.285714286).
Square it (18.36734694) and add it to both sides.

Add '18.36734694' to each side of the equation.
-8.571428571x + 18.36734694 + x2 = -4.081632653 + 18.36734694

Reorder the terms:
18.36734694 + -8.571428571x + x2 = -4.081632653 + 18.36734694

Combine like terms: -4.081632653 + 18.36734694 = 14.285714287
18.36734694 + -8.571428571x + x2 = 14.285714287

Factor a perfect square on the left side:
(x + -4.285714286)(x + -4.285714286) = 14.285714287

Calculate the square root of the right side: 3.77964473

Break this problem into two subproblems by setting 
(x + -4.285714286) equal to 3.77964473 and -3.77964473.

Subproblem 1

x + -4.285714286 = 3.77964473 Simplifying x + -4.285714286 = 3.77964473 Reorder the terms: -4.285714286 + x = 3.77964473 Solving -4.285714286 + x = 3.77964473 Solving for variable 'x'. Move all terms containing x to the left, all other terms to the right. Add '4.285714286' to each side of the equation. -4.285714286 + 4.285714286 + x = 3.77964473 + 4.285714286 Combine like terms: -4.285714286 + 4.285714286 = 0.000000000 0.000000000 + x = 3.77964473 + 4.285714286 x = 3.77964473 + 4.285714286 Combine like terms: 3.77964473 + 4.285714286 = 8.065359016 x = 8.065359016 Simplifying x = 8.065359016

Subproblem 2

x + -4.285714286 = -3.77964473 Simplifying x + -4.285714286 = -3.77964473 Reorder the terms: -4.285714286 + x = -3.77964473 Solving -4.285714286 + x = -3.77964473 Solving for variable 'x'. Move all terms containing x to the left, all other terms to the right. Add '4.285714286' to each side of the equation. -4.285714286 + 4.285714286 + x = -3.77964473 + 4.285714286 Combine like terms: -4.285714286 + 4.285714286 = 0.000000000 0.000000000 + x = -3.77964473 + 4.285714286 x = -3.77964473 + 4.285714286 Combine like terms: -3.77964473 + 4.285714286 = 0.506069556 x = 0.506069556 Simplifying x = 0.506069556

Solution

The solution to the problem is based on the solutions from the subproblems. x = {8.065359016, 0.506069556}

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