7x^2+3x+5=21

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Solution for 7x^2+3x+5=21 equation:


Simplifying
7x2 + 3x + 5 = 21

Reorder the terms:
5 + 3x + 7x2 = 21

Solving
5 + 3x + 7x2 = 21

Solving for variable 'x'.

Reorder the terms:
5 + -21 + 3x + 7x2 = 21 + -21

Combine like terms: 5 + -21 = -16
-16 + 3x + 7x2 = 21 + -21

Combine like terms: 21 + -21 = 0
-16 + 3x + 7x2 = 0

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

Divide each side by '7'.
-2.285714286 + 0.4285714286x + x2 = 0

Move the constant term to the right:

Add '2.285714286' to each side of the equation.
-2.285714286 + 0.4285714286x + 2.285714286 + x2 = 0 + 2.285714286

Reorder the terms:
-2.285714286 + 2.285714286 + 0.4285714286x + x2 = 0 + 2.285714286

Combine like terms: -2.285714286 + 2.285714286 = 0.000000000
0.000000000 + 0.4285714286x + x2 = 0 + 2.285714286
0.4285714286x + x2 = 0 + 2.285714286

Combine like terms: 0 + 2.285714286 = 2.285714286
0.4285714286x + x2 = 2.285714286

The x term is 0.4285714286x.  Take half its coefficient (0.2142857143).
Square it (0.04591836735) and add it to both sides.

Add '0.04591836735' to each side of the equation.
0.4285714286x + 0.04591836735 + x2 = 2.285714286 + 0.04591836735

Reorder the terms:
0.04591836735 + 0.4285714286x + x2 = 2.285714286 + 0.04591836735

Combine like terms: 2.285714286 + 0.04591836735 = 2.33163265335
0.04591836735 + 0.4285714286x + x2 = 2.33163265335

Factor a perfect square on the left side:
(x + 0.2142857143)(x + 0.2142857143) = 2.33163265335

Calculate the square root of the right side: 1.526968452

Break this problem into two subproblems by setting 
(x + 0.2142857143) equal to 1.526968452 and -1.526968452.

Subproblem 1

x + 0.2142857143 = 1.526968452 Simplifying x + 0.2142857143 = 1.526968452 Reorder the terms: 0.2142857143 + x = 1.526968452 Solving 0.2142857143 + x = 1.526968452 Solving for variable 'x'. Move all terms containing x to the left, all other terms to the right. Add '-0.2142857143' to each side of the equation. 0.2142857143 + -0.2142857143 + x = 1.526968452 + -0.2142857143 Combine like terms: 0.2142857143 + -0.2142857143 = 0.0000000000 0.0000000000 + x = 1.526968452 + -0.2142857143 x = 1.526968452 + -0.2142857143 Combine like terms: 1.526968452 + -0.2142857143 = 1.3126827377 x = 1.3126827377 Simplifying x = 1.3126827377

Subproblem 2

x + 0.2142857143 = -1.526968452 Simplifying x + 0.2142857143 = -1.526968452 Reorder the terms: 0.2142857143 + x = -1.526968452 Solving 0.2142857143 + x = -1.526968452 Solving for variable 'x'. Move all terms containing x to the left, all other terms to the right. Add '-0.2142857143' to each side of the equation. 0.2142857143 + -0.2142857143 + x = -1.526968452 + -0.2142857143 Combine like terms: 0.2142857143 + -0.2142857143 = 0.0000000000 0.0000000000 + x = -1.526968452 + -0.2142857143 x = -1.526968452 + -0.2142857143 Combine like terms: -1.526968452 + -0.2142857143 = -1.7412541663 x = -1.7412541663 Simplifying x = -1.7412541663

Solution

The solution to the problem is based on the solutions from the subproblems. x = {1.3126827377, -1.7412541663}

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