x^2-78x-15=0

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


Simplifying
x2 + -78x + -15 = 0

Reorder the terms:
-15 + -78x + x2 = 0

Solving
-15 + -78x + x2 = 0

Solving for variable 'x'.

Begin completing the square.

Move the constant term to the right:

Add '15' to each side of the equation.
-15 + -78x + 15 + x2 = 0 + 15

Reorder the terms:
-15 + 15 + -78x + x2 = 0 + 15

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

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

The x term is -78x.  Take half its coefficient (-39).
Square it (1521) and add it to both sides.

Add '1521' to each side of the equation.
-78x + 1521 + x2 = 15 + 1521

Reorder the terms:
1521 + -78x + x2 = 15 + 1521

Combine like terms: 15 + 1521 = 1536
1521 + -78x + x2 = 1536

Factor a perfect square on the left side:
(x + -39)(x + -39) = 1536

Calculate the square root of the right side: 39.191835885

Break this problem into two subproblems by setting 
(x + -39) equal to 39.191835885 and -39.191835885.

Subproblem 1

x + -39 = 39.191835885 Simplifying x + -39 = 39.191835885 Reorder the terms: -39 + x = 39.191835885 Solving -39 + x = 39.191835885 Solving for variable 'x'. Move all terms containing x to the left, all other terms to the right. Add '39' to each side of the equation. -39 + 39 + x = 39.191835885 + 39 Combine like terms: -39 + 39 = 0 0 + x = 39.191835885 + 39 x = 39.191835885 + 39 Combine like terms: 39.191835885 + 39 = 78.191835885 x = 78.191835885 Simplifying x = 78.191835885

Subproblem 2

x + -39 = -39.191835885 Simplifying x + -39 = -39.191835885 Reorder the terms: -39 + x = -39.191835885 Solving -39 + x = -39.191835885 Solving for variable 'x'. Move all terms containing x to the left, all other terms to the right. Add '39' to each side of the equation. -39 + 39 + x = -39.191835885 + 39 Combine like terms: -39 + 39 = 0 0 + x = -39.191835885 + 39 x = -39.191835885 + 39 Combine like terms: -39.191835885 + 39 = -0.191835885 x = -0.191835885 Simplifying x = -0.191835885

Solution

The solution to the problem is based on the solutions from the subproblems. x = {78.191835885, -0.191835885}

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