3x^2-7x-21=0

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Solution for 3x^2-7x-21=0 equation: 


Simplifying
3x2 + -7x + -21 = 0

Reorder the terms:
-21 + -7x + 3x2 = 0

Solving
-21 + -7x + 3x2 = 0

Solving for variable 'x'.

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

Divide each side by '3'.
-7 + -2.333333333x + x2 = 0

Move the constant term to the right:

Add '7' to each side of the equation.
-7 + -2.333333333x + 7 + x2 = 0 + 7

Reorder the terms:
-7 + 7 + -2.333333333x + x2 = 0 + 7

Combine like terms: -7 + 7 = 0
0 + -2.333333333x + x2 = 0 + 7
-2.333333333x + x2 = 0 + 7

Combine like terms: 0 + 7 = 7
-2.333333333x + x2 = 7

The x term is -2.333333333x.  Take half its coefficient (-1.166666667).
Square it (1.361111112) and add it to both sides.

Add '1.361111112' to each side of the equation.
-2.333333333x + 1.361111112 + x2 = 7 + 1.361111112

Reorder the terms:
1.361111112 + -2.333333333x + x2 = 7 + 1.361111112

Combine like terms: 7 + 1.361111112 = 8.361111112
1.361111112 + -2.333333333x + x2 = 8.361111112

Factor a perfect square on the left side:
(x + -1.166666667)(x + -1.166666667) = 8.361111112

Calculate the square root of the right side: 2.891558596

Break this problem into two subproblems by setting 
(x + -1.166666667) equal to 2.891558596 and -2.891558596.


Subproblem 1
x + -1.166666667 = 2.891558596

Simplifying
x + -1.166666667 = 2.891558596

Reorder the terms:
-1.166666667 + x = 2.891558596

Solving
-1.166666667 + x = 2.891558596

Solving for variable 'x'.

Move all terms containing x to the left, all other terms to the right.

Add '1.166666667' to each side of the equation.
-1.166666667 + 1.166666667 + x = 2.891558596 + 1.166666667

Combine like terms: -1.166666667 + 1.166666667 = 0.000000000
0.000000000 + x = 2.891558596 + 1.166666667
x = 2.891558596 + 1.166666667

Combine like terms: 2.891558596 + 1.166666667 = 4.058225263
x = 4.058225263

Simplifying
x = 4.058225263


Subproblem 2
x + -1.166666667 = -2.891558596

Simplifying
x + -1.166666667 = -2.891558596

Reorder the terms:
-1.166666667 + x = -2.891558596

Solving
-1.166666667 + x = -2.891558596

Solving for variable 'x'.

Move all terms containing x to the left, all other terms to the right.

Add '1.166666667' to each side of the equation.
-1.166666667 + 1.166666667 + x = -2.891558596 + 1.166666667

Combine like terms: -1.166666667 + 1.166666667 = 0.000000000
0.000000000 + x = -2.891558596 + 1.166666667
x = -2.891558596 + 1.166666667

Combine like terms: -2.891558596 + 1.166666667 = -1.724891929
x = -1.724891929

Simplifying
x = -1.724891929


Solution
The solution to the problem is based on the solutions
from the subproblems.
x = {4.058225263, -1.724891929}

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