u^2-3u-15=0

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Solution for u^2-3u-15=0 equation:


Simplifying
u2 + -3u + -15 = 0

Reorder the terms:
-15 + -3u + u2 = 0

Solving
-15 + -3u + u2 = 0

Solving for variable 'u'.

Begin completing the square.

Move the constant term to the right:

Add '15' to each side of the equation.
-15 + -3u + 15 + u2 = 0 + 15

Reorder the terms:
-15 + 15 + -3u + u2 = 0 + 15

Combine like terms: -15 + 15 = 0
0 + -3u + u2 = 0 + 15
-3u + u2 = 0 + 15

Combine like terms: 0 + 15 = 15
-3u + u2 = 15

The u term is -3u.  Take half its coefficient (-1.5).
Square it (2.25) and add it to both sides.

Add '2.25' to each side of the equation.
-3u + 2.25 + u2 = 15 + 2.25

Reorder the terms:
2.25 + -3u + u2 = 15 + 2.25

Combine like terms: 15 + 2.25 = 17.25
2.25 + -3u + u2 = 17.25

Factor a perfect square on the left side:
(u + -1.5)(u + -1.5) = 17.25

Calculate the square root of the right side: 4.153311931

Break this problem into two subproblems by setting 
(u + -1.5) equal to 4.153311931 and -4.153311931.

Subproblem 1

u + -1.5 = 4.153311931 Simplifying u + -1.5 = 4.153311931 Reorder the terms: -1.5 + u = 4.153311931 Solving -1.5 + u = 4.153311931 Solving for variable 'u'. Move all terms containing u to the left, all other terms to the right. Add '1.5' to each side of the equation. -1.5 + 1.5 + u = 4.153311931 + 1.5 Combine like terms: -1.5 + 1.5 = 0.0 0.0 + u = 4.153311931 + 1.5 u = 4.153311931 + 1.5 Combine like terms: 4.153311931 + 1.5 = 5.653311931 u = 5.653311931 Simplifying u = 5.653311931

Subproblem 2

u + -1.5 = -4.153311931 Simplifying u + -1.5 = -4.153311931 Reorder the terms: -1.5 + u = -4.153311931 Solving -1.5 + u = -4.153311931 Solving for variable 'u'. Move all terms containing u to the left, all other terms to the right. Add '1.5' to each side of the equation. -1.5 + 1.5 + u = -4.153311931 + 1.5 Combine like terms: -1.5 + 1.5 = 0.0 0.0 + u = -4.153311931 + 1.5 u = -4.153311931 + 1.5 Combine like terms: -4.153311931 + 1.5 = -2.653311931 u = -2.653311931 Simplifying u = -2.653311931

Solution

The solution to the problem is based on the solutions from the subproblems. u = {5.653311931, -2.653311931}

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