7x^2+11x-21=0

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Solution for 7x^2+11x-21=0 equation:


Simplifying
7x2 + 11x + -21 = 0

Reorder the terms:
-21 + 11x + 7x2 = 0

Solving
-21 + 11x + 7x2 = 0

Solving for variable 'x'.

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

Divide each side by '7'.
-3 + 1.571428571x + x2 = 0

Move the constant term to the right:

Add '3' to each side of the equation.
-3 + 1.571428571x + 3 + x2 = 0 + 3

Reorder the terms:
-3 + 3 + 1.571428571x + x2 = 0 + 3

Combine like terms: -3 + 3 = 0
0 + 1.571428571x + x2 = 0 + 3
1.571428571x + x2 = 0 + 3

Combine like terms: 0 + 3 = 3
1.571428571x + x2 = 3

The x term is 1.571428571x.  Take half its coefficient (0.7857142855).
Square it (0.6173469384) and add it to both sides.

Add '0.6173469384' to each side of the equation.
1.571428571x + 0.6173469384 + x2 = 3 + 0.6173469384

Reorder the terms:
0.6173469384 + 1.571428571x + x2 = 3 + 0.6173469384

Combine like terms: 3 + 0.6173469384 = 3.6173469384
0.6173469384 + 1.571428571x + x2 = 3.6173469384

Factor a perfect square on the left side:
(x + 0.7857142855)(x + 0.7857142855) = 3.6173469384

Calculate the square root of the right side: 1.901932422

Break this problem into two subproblems by setting 
(x + 0.7857142855) equal to 1.901932422 and -1.901932422.

Subproblem 1

x + 0.7857142855 = 1.901932422 Simplifying x + 0.7857142855 = 1.901932422 Reorder the terms: 0.7857142855 + x = 1.901932422 Solving 0.7857142855 + x = 1.901932422 Solving for variable 'x'. Move all terms containing x to the left, all other terms to the right. Add '-0.7857142855' to each side of the equation. 0.7857142855 + -0.7857142855 + x = 1.901932422 + -0.7857142855 Combine like terms: 0.7857142855 + -0.7857142855 = 0.0000000000 0.0000000000 + x = 1.901932422 + -0.7857142855 x = 1.901932422 + -0.7857142855 Combine like terms: 1.901932422 + -0.7857142855 = 1.1162181365 x = 1.1162181365 Simplifying x = 1.1162181365

Subproblem 2

x + 0.7857142855 = -1.901932422 Simplifying x + 0.7857142855 = -1.901932422 Reorder the terms: 0.7857142855 + x = -1.901932422 Solving 0.7857142855 + x = -1.901932422 Solving for variable 'x'. Move all terms containing x to the left, all other terms to the right. Add '-0.7857142855' to each side of the equation. 0.7857142855 + -0.7857142855 + x = -1.901932422 + -0.7857142855 Combine like terms: 0.7857142855 + -0.7857142855 = 0.0000000000 0.0000000000 + x = -1.901932422 + -0.7857142855 x = -1.901932422 + -0.7857142855 Combine like terms: -1.901932422 + -0.7857142855 = -2.6876467075 x = -2.6876467075 Simplifying x = -2.6876467075

Solution

The solution to the problem is based on the solutions from the subproblems. x = {1.1162181365, -2.6876467075}

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