3.9=18x-4.9x^2

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Solution for 3.9=18x-4.9x^2 equation:


Simplifying
3.9 = 18x + -4.9x2

Solving
3.9 = 18x + -4.9x2

Solving for variable 'x'.

Reorder the terms:
3.9 + -18x + 4.9x2 = 18x + -18x + -4.9x2 + 4.9x2

Combine like terms: 18x + -18x = 0
3.9 + -18x + 4.9x2 = 0 + -4.9x2 + 4.9x2
3.9 + -18x + 4.9x2 = -4.9x2 + 4.9x2

Combine like terms: -4.9x2 + 4.9x2 = 0.0
3.9 + -18x + 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'.
0.7959183673 + -3.673469388x + x2 = 0

Move the constant term to the right:

Add '-0.7959183673' to each side of the equation.
0.7959183673 + -3.673469388x + -0.7959183673 + x2 = 0 + -0.7959183673

Reorder the terms:
0.7959183673 + -0.7959183673 + -3.673469388x + x2 = 0 + -0.7959183673

Combine like terms: 0.7959183673 + -0.7959183673 = 0.0000000000
0.0000000000 + -3.673469388x + x2 = 0 + -0.7959183673
-3.673469388x + x2 = 0 + -0.7959183673

Combine like terms: 0 + -0.7959183673 = -0.7959183673
-3.673469388x + x2 = -0.7959183673

The x term is -3.673469388x.  Take half its coefficient (-1.836734694).
Square it (3.373594336) and add it to both sides.

Add '3.373594336' to each side of the equation.
-3.673469388x + 3.373594336 + x2 = -0.7959183673 + 3.373594336

Reorder the terms:
3.373594336 + -3.673469388x + x2 = -0.7959183673 + 3.373594336

Combine like terms: -0.7959183673 + 3.373594336 = 2.5776759687
3.373594336 + -3.673469388x + x2 = 2.5776759687

Factor a perfect square on the left side:
(x + -1.836734694)(x + -1.836734694) = 2.5776759687

Calculate the square root of the right side: 1.605514238

Break this problem into two subproblems by setting 
(x + -1.836734694) equal to 1.605514238 and -1.605514238.

Subproblem 1

x + -1.836734694 = 1.605514238 Simplifying x + -1.836734694 = 1.605514238 Reorder the terms: -1.836734694 + x = 1.605514238 Solving -1.836734694 + x = 1.605514238 Solving for variable 'x'. Move all terms containing x to the left, all other terms to the right. Add '1.836734694' to each side of the equation. -1.836734694 + 1.836734694 + x = 1.605514238 + 1.836734694 Combine like terms: -1.836734694 + 1.836734694 = 0.000000000 0.000000000 + x = 1.605514238 + 1.836734694 x = 1.605514238 + 1.836734694 Combine like terms: 1.605514238 + 1.836734694 = 3.442248932 x = 3.442248932 Simplifying x = 3.442248932

Subproblem 2

x + -1.836734694 = -1.605514238 Simplifying x + -1.836734694 = -1.605514238 Reorder the terms: -1.836734694 + x = -1.605514238 Solving -1.836734694 + x = -1.605514238 Solving for variable 'x'. Move all terms containing x to the left, all other terms to the right. Add '1.836734694' to each side of the equation. -1.836734694 + 1.836734694 + x = -1.605514238 + 1.836734694 Combine like terms: -1.836734694 + 1.836734694 = 0.000000000 0.000000000 + x = -1.605514238 + 1.836734694 x = -1.605514238 + 1.836734694 Combine like terms: -1.605514238 + 1.836734694 = 0.231220456 x = 0.231220456 Simplifying x = 0.231220456

Solution

The solution to the problem is based on the solutions from the subproblems. x = {3.442248932, 0.231220456}

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