-7x^2-6x+21=0

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Solution for -7x^2-6x+21=0 equation:


Simplifying
-7x2 + -6x + 21 = 0

Reorder the terms:
21 + -6x + -7x2 = 0

Solving
21 + -6x + -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 + 0.8571428571x + x2 = 0

Move the constant term to the right:

Add '3' to each side of the equation.
-3 + 0.8571428571x + 3 + x2 = 0 + 3

Reorder the terms:
-3 + 3 + 0.8571428571x + x2 = 0 + 3

Combine like terms: -3 + 3 = 0
0 + 0.8571428571x + x2 = 0 + 3
0.8571428571x + x2 = 0 + 3

Combine like terms: 0 + 3 = 3
0.8571428571x + x2 = 3

The x term is 0.8571428571x.  Take half its coefficient (0.4285714286).
Square it (0.1836734694) and add it to both sides.

Add '0.1836734694' to each side of the equation.
0.8571428571x + 0.1836734694 + x2 = 3 + 0.1836734694

Reorder the terms:
0.1836734694 + 0.8571428571x + x2 = 3 + 0.1836734694

Combine like terms: 3 + 0.1836734694 = 3.1836734694
0.1836734694 + 0.8571428571x + x2 = 3.1836734694

Factor a perfect square on the left side:
(x + 0.4285714286)(x + 0.4285714286) = 3.1836734694

Calculate the square root of the right side: 1.784285142

Break this problem into two subproblems by setting 
(x + 0.4285714286) equal to 1.784285142 and -1.784285142.

Subproblem 1

x + 0.4285714286 = 1.784285142 Simplifying x + 0.4285714286 = 1.784285142 Reorder the terms: 0.4285714286 + x = 1.784285142 Solving 0.4285714286 + x = 1.784285142 Solving for variable 'x'. Move all terms containing x to the left, all other terms to the right. Add '-0.4285714286' to each side of the equation. 0.4285714286 + -0.4285714286 + x = 1.784285142 + -0.4285714286 Combine like terms: 0.4285714286 + -0.4285714286 = 0.0000000000 0.0000000000 + x = 1.784285142 + -0.4285714286 x = 1.784285142 + -0.4285714286 Combine like terms: 1.784285142 + -0.4285714286 = 1.3557137134 x = 1.3557137134 Simplifying x = 1.3557137134

Subproblem 2

x + 0.4285714286 = -1.784285142 Simplifying x + 0.4285714286 = -1.784285142 Reorder the terms: 0.4285714286 + x = -1.784285142 Solving 0.4285714286 + x = -1.784285142 Solving for variable 'x'. Move all terms containing x to the left, all other terms to the right. Add '-0.4285714286' to each side of the equation. 0.4285714286 + -0.4285714286 + x = -1.784285142 + -0.4285714286 Combine like terms: 0.4285714286 + -0.4285714286 = 0.0000000000 0.0000000000 + x = -1.784285142 + -0.4285714286 x = -1.784285142 + -0.4285714286 Combine like terms: -1.784285142 + -0.4285714286 = -2.2128565706 x = -2.2128565706 Simplifying x = -2.2128565706

Solution

The solution to the problem is based on the solutions from the subproblems. x = {1.3557137134, -2.2128565706}

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