0=78+15x-4.9x^2

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Solution for 0=78+15x-4.9x^2 equation:


Simplifying
0 = 78 + 15x + -4.9x2

Solving
0 = 78 + 15x + -4.9x2

Solving for variable 'x'.

Combine like terms: 0 + -78 = -78
-78 + -15x + 4.9x2 = 78 + 15x + -4.9x2 + -78 + -15x + 4.9x2

Reorder the terms:
-78 + -15x + 4.9x2 = 78 + -78 + 15x + -15x + -4.9x2 + 4.9x2

Combine like terms: 78 + -78 = 0
-78 + -15x + 4.9x2 = 0 + 15x + -15x + -4.9x2 + 4.9x2
-78 + -15x + 4.9x2 = 15x + -15x + -4.9x2 + 4.9x2

Combine like terms: 15x + -15x = 0
-78 + -15x + 4.9x2 = 0 + -4.9x2 + 4.9x2
-78 + -15x + 4.9x2 = -4.9x2 + 4.9x2

Combine like terms: -4.9x2 + 4.9x2 = 0.0
-78 + -15x + 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'.
-15.91836735 + -3.06122449x + x2 = 0

Move the constant term to the right:

Add '15.91836735' to each side of the equation.
-15.91836735 + -3.06122449x + 15.91836735 + x2 = 0 + 15.91836735

Reorder the terms:
-15.91836735 + 15.91836735 + -3.06122449x + x2 = 0 + 15.91836735

Combine like terms: -15.91836735 + 15.91836735 = 0.00000000
0.00000000 + -3.06122449x + x2 = 0 + 15.91836735
-3.06122449x + x2 = 0 + 15.91836735

Combine like terms: 0 + 15.91836735 = 15.91836735
-3.06122449x + x2 = 15.91836735

The x term is -3.06122449x.  Take half its coefficient (-1.530612245).
Square it (2.342773845) and add it to both sides.

Add '2.342773845' to each side of the equation.
-3.06122449x + 2.342773845 + x2 = 15.91836735 + 2.342773845

Reorder the terms:
2.342773845 + -3.06122449x + x2 = 15.91836735 + 2.342773845

Combine like terms: 15.91836735 + 2.342773845 = 18.261141195
2.342773845 + -3.06122449x + x2 = 18.261141195

Factor a perfect square on the left side:
(x + -1.530612245)(x + -1.530612245) = 18.261141195

Calculate the square root of the right side: 4.273305652

Break this problem into two subproblems by setting 
(x + -1.530612245) equal to 4.273305652 and -4.273305652.

Subproblem 1

x + -1.530612245 = 4.273305652 Simplifying x + -1.530612245 = 4.273305652 Reorder the terms: -1.530612245 + x = 4.273305652 Solving -1.530612245 + x = 4.273305652 Solving for variable 'x'. Move all terms containing x to the left, all other terms to the right. Add '1.530612245' to each side of the equation. -1.530612245 + 1.530612245 + x = 4.273305652 + 1.530612245 Combine like terms: -1.530612245 + 1.530612245 = 0.000000000 0.000000000 + x = 4.273305652 + 1.530612245 x = 4.273305652 + 1.530612245 Combine like terms: 4.273305652 + 1.530612245 = 5.803917897 x = 5.803917897 Simplifying x = 5.803917897

Subproblem 2

x + -1.530612245 = -4.273305652 Simplifying x + -1.530612245 = -4.273305652 Reorder the terms: -1.530612245 + x = -4.273305652 Solving -1.530612245 + x = -4.273305652 Solving for variable 'x'. Move all terms containing x to the left, all other terms to the right. Add '1.530612245' to each side of the equation. -1.530612245 + 1.530612245 + x = -4.273305652 + 1.530612245 Combine like terms: -1.530612245 + 1.530612245 = 0.000000000 0.000000000 + x = -4.273305652 + 1.530612245 x = -4.273305652 + 1.530612245 Combine like terms: -4.273305652 + 1.530612245 = -2.742693407 x = -2.742693407 Simplifying x = -2.742693407

Solution

The solution to the problem is based on the solutions from the subproblems. x = {5.803917897, -2.742693407}

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