x^2-15x+21=0

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Solution for x^2-15x+21=0 equation:


Simplifying
x2 + -15x + 21 = 0

Reorder the terms:
21 + -15x + x2 = 0

Solving
21 + -15x + x2 = 0

Solving for variable 'x'.

Begin completing the square.

Move the constant term to the right:

Add '-21' to each side of the equation.
21 + -15x + -21 + x2 = 0 + -21

Reorder the terms:
21 + -21 + -15x + x2 = 0 + -21

Combine like terms: 21 + -21 = 0
0 + -15x + x2 = 0 + -21
-15x + x2 = 0 + -21

Combine like terms: 0 + -21 = -21
-15x + x2 = -21

The x term is -15x.  Take half its coefficient (-7.5).
Square it (56.25) and add it to both sides.

Add '56.25' to each side of the equation.
-15x + 56.25 + x2 = -21 + 56.25

Reorder the terms:
56.25 + -15x + x2 = -21 + 56.25

Combine like terms: -21 + 56.25 = 35.25
56.25 + -15x + x2 = 35.25

Factor a perfect square on the left side:
(x + -7.5)(x + -7.5) = 35.25

Calculate the square root of the right side: 5.937171044

Break this problem into two subproblems by setting 
(x + -7.5) equal to 5.937171044 and -5.937171044.

Subproblem 1

x + -7.5 = 5.937171044 Simplifying x + -7.5 = 5.937171044 Reorder the terms: -7.5 + x = 5.937171044 Solving -7.5 + x = 5.937171044 Solving for variable 'x'. Move all terms containing x to the left, all other terms to the right. Add '7.5' to each side of the equation. -7.5 + 7.5 + x = 5.937171044 + 7.5 Combine like terms: -7.5 + 7.5 = 0.0 0.0 + x = 5.937171044 + 7.5 x = 5.937171044 + 7.5 Combine like terms: 5.937171044 + 7.5 = 13.437171044 x = 13.437171044 Simplifying x = 13.437171044

Subproblem 2

x + -7.5 = -5.937171044 Simplifying x + -7.5 = -5.937171044 Reorder the terms: -7.5 + x = -5.937171044 Solving -7.5 + x = -5.937171044 Solving for variable 'x'. Move all terms containing x to the left, all other terms to the right. Add '7.5' to each side of the equation. -7.5 + 7.5 + x = -5.937171044 + 7.5 Combine like terms: -7.5 + 7.5 = 0.0 0.0 + x = -5.937171044 + 7.5 x = -5.937171044 + 7.5 Combine like terms: -5.937171044 + 7.5 = 1.562828956 x = 1.562828956 Simplifying x = 1.562828956

Solution

The solution to the problem is based on the solutions from the subproblems. x = {13.437171044, 1.562828956}

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