5x^2-28x+21=0

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Solution for 5x^2-28x+21=0 equation:


Simplifying
5x2 + -28x + 21 = 0

Reorder the terms:
21 + -28x + 5x2 = 0

Solving
21 + -28x + 5x2 = 0

Solving for variable 'x'.

Begin completing the square.  Divide all terms by
5 the coefficient of the squared term: 

Divide each side by '5'.
4.2 + -5.6x + x2 = 0

Move the constant term to the right:

Add '-4.2' to each side of the equation.
4.2 + -5.6x + -4.2 + x2 = 0 + -4.2

Reorder the terms:
4.2 + -4.2 + -5.6x + x2 = 0 + -4.2

Combine like terms: 4.2 + -4.2 = 0.0
0.0 + -5.6x + x2 = 0 + -4.2
-5.6x + x2 = 0 + -4.2

Combine like terms: 0 + -4.2 = -4.2
-5.6x + x2 = -4.2

The x term is -5.6x.  Take half its coefficient (-2.8).
Square it (7.84) and add it to both sides.

Add '7.84' to each side of the equation.
-5.6x + 7.84 + x2 = -4.2 + 7.84

Reorder the terms:
7.84 + -5.6x + x2 = -4.2 + 7.84

Combine like terms: -4.2 + 7.84 = 3.64
7.84 + -5.6x + x2 = 3.64

Factor a perfect square on the left side:
(x + -2.8)(x + -2.8) = 3.64

Calculate the square root of the right side: 1.907878403

Break this problem into two subproblems by setting 
(x + -2.8) equal to 1.907878403 and -1.907878403.

Subproblem 1

x + -2.8 = 1.907878403 Simplifying x + -2.8 = 1.907878403 Reorder the terms: -2.8 + x = 1.907878403 Solving -2.8 + x = 1.907878403 Solving for variable 'x'. Move all terms containing x to the left, all other terms to the right. Add '2.8' to each side of the equation. -2.8 + 2.8 + x = 1.907878403 + 2.8 Combine like terms: -2.8 + 2.8 = 0.0 0.0 + x = 1.907878403 + 2.8 x = 1.907878403 + 2.8 Combine like terms: 1.907878403 + 2.8 = 4.707878403 x = 4.707878403 Simplifying x = 4.707878403

Subproblem 2

x + -2.8 = -1.907878403 Simplifying x + -2.8 = -1.907878403 Reorder the terms: -2.8 + x = -1.907878403 Solving -2.8 + x = -1.907878403 Solving for variable 'x'. Move all terms containing x to the left, all other terms to the right. Add '2.8' to each side of the equation. -2.8 + 2.8 + x = -1.907878403 + 2.8 Combine like terms: -2.8 + 2.8 = 0.0 0.0 + x = -1.907878403 + 2.8 x = -1.907878403 + 2.8 Combine like terms: -1.907878403 + 2.8 = 0.892121597 x = 0.892121597 Simplifying x = 0.892121597

Solution

The solution to the problem is based on the solutions from the subproblems. x = {4.707878403, 0.892121597}

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