5x^2+3x=21

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Solution for 5x^2+3x=21 equation:


Simplifying
5x2 + 3x = 21

Reorder the terms:
3x + 5x2 = 21

Solving
3x + 5x2 = 21

Solving for variable 'x'.

Reorder the terms:
-21 + 3x + 5x2 = 21 + -21

Combine like terms: 21 + -21 = 0
-21 + 3x + 5x2 = 0

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

Divide each side by '5'.
-4.2 + 0.6x + x2 = 0

Move the constant term to the right:

Add '4.2' to each side of the equation.
-4.2 + 0.6x + 4.2 + x2 = 0 + 4.2

Reorder the terms:
-4.2 + 4.2 + 0.6x + x2 = 0 + 4.2

Combine like terms: -4.2 + 4.2 = 0.0
0.0 + 0.6x + x2 = 0 + 4.2
0.6x + x2 = 0 + 4.2

Combine like terms: 0 + 4.2 = 4.2
0.6x + x2 = 4.2

The x term is 0.6x.  Take half its coefficient (0.3).
Square it (0.09) and add it to both sides.

Add '0.09' to each side of the equation.
0.6x + 0.09 + x2 = 4.2 + 0.09

Reorder the terms:
0.09 + 0.6x + x2 = 4.2 + 0.09

Combine like terms: 4.2 + 0.09 = 4.29
0.09 + 0.6x + x2 = 4.29

Factor a perfect square on the left side:
(x + 0.3)(x + 0.3) = 4.29

Calculate the square root of the right side: 2.071231518

Break this problem into two subproblems by setting 
(x + 0.3) equal to 2.071231518 and -2.071231518.

Subproblem 1

x + 0.3 = 2.071231518 Simplifying x + 0.3 = 2.071231518 Reorder the terms: 0.3 + x = 2.071231518 Solving 0.3 + x = 2.071231518 Solving for variable 'x'. Move all terms containing x to the left, all other terms to the right. Add '-0.3' to each side of the equation. 0.3 + -0.3 + x = 2.071231518 + -0.3 Combine like terms: 0.3 + -0.3 = 0.0 0.0 + x = 2.071231518 + -0.3 x = 2.071231518 + -0.3 Combine like terms: 2.071231518 + -0.3 = 1.771231518 x = 1.771231518 Simplifying x = 1.771231518

Subproblem 2

x + 0.3 = -2.071231518 Simplifying x + 0.3 = -2.071231518 Reorder the terms: 0.3 + x = -2.071231518 Solving 0.3 + x = -2.071231518 Solving for variable 'x'. Move all terms containing x to the left, all other terms to the right. Add '-0.3' to each side of the equation. 0.3 + -0.3 + x = -2.071231518 + -0.3 Combine like terms: 0.3 + -0.3 = 0.0 0.0 + x = -2.071231518 + -0.3 x = -2.071231518 + -0.3 Combine like terms: -2.071231518 + -0.3 = -2.371231518 x = -2.371231518 Simplifying x = -2.371231518

Solution

The solution to the problem is based on the solutions from the subproblems. x = {1.771231518, -2.371231518}

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