3x^2+10x=21

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Solution for 3x^2+10x=21 equation:


Simplifying
3x2 + 10x = 21

Reorder the terms:
10x + 3x2 = 21

Solving
10x + 3x2 = 21

Solving for variable 'x'.

Reorder the terms:
-21 + 10x + 3x2 = 21 + -21

Combine like terms: 21 + -21 = 0
-21 + 10x + 3x2 = 0

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

Divide each side by '3'.
-7 + 3.333333333x + x2 = 0

Move the constant term to the right:

Add '7' to each side of the equation.
-7 + 3.333333333x + 7 + x2 = 0 + 7

Reorder the terms:
-7 + 7 + 3.333333333x + x2 = 0 + 7

Combine like terms: -7 + 7 = 0
0 + 3.333333333x + x2 = 0 + 7
3.333333333x + x2 = 0 + 7

Combine like terms: 0 + 7 = 7
3.333333333x + x2 = 7

The x term is 3.333333333x.  Take half its coefficient (1.666666667).
Square it (2.777777779) and add it to both sides.

Add '2.777777779' to each side of the equation.
3.333333333x + 2.777777779 + x2 = 7 + 2.777777779

Reorder the terms:
2.777777779 + 3.333333333x + x2 = 7 + 2.777777779

Combine like terms: 7 + 2.777777779 = 9.777777779
2.777777779 + 3.333333333x + x2 = 9.777777779

Factor a perfect square on the left side:
(x + 1.666666667)(x + 1.666666667) = 9.777777779

Calculate the square root of the right side: 3.12694384

Break this problem into two subproblems by setting 
(x + 1.666666667) equal to 3.12694384 and -3.12694384.

Subproblem 1

x + 1.666666667 = 3.12694384 Simplifying x + 1.666666667 = 3.12694384 Reorder the terms: 1.666666667 + x = 3.12694384 Solving 1.666666667 + x = 3.12694384 Solving for variable 'x'. Move all terms containing x to the left, all other terms to the right. Add '-1.666666667' to each side of the equation. 1.666666667 + -1.666666667 + x = 3.12694384 + -1.666666667 Combine like terms: 1.666666667 + -1.666666667 = 0.000000000 0.000000000 + x = 3.12694384 + -1.666666667 x = 3.12694384 + -1.666666667 Combine like terms: 3.12694384 + -1.666666667 = 1.460277173 x = 1.460277173 Simplifying x = 1.460277173

Subproblem 2

x + 1.666666667 = -3.12694384 Simplifying x + 1.666666667 = -3.12694384 Reorder the terms: 1.666666667 + x = -3.12694384 Solving 1.666666667 + x = -3.12694384 Solving for variable 'x'. Move all terms containing x to the left, all other terms to the right. Add '-1.666666667' to each side of the equation. 1.666666667 + -1.666666667 + x = -3.12694384 + -1.666666667 Combine like terms: 1.666666667 + -1.666666667 = 0.000000000 0.000000000 + x = -3.12694384 + -1.666666667 x = -3.12694384 + -1.666666667 Combine like terms: -3.12694384 + -1.666666667 = -4.793610507 x = -4.793610507 Simplifying x = -4.793610507

Solution

The solution to the problem is based on the solutions from the subproblems. x = {1.460277173, -4.793610507}

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