15x+6x^2-21+x^2=

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Solution for 15x+6x^2-21+x^2= equation:


Simplifying
15x + 6x2 + -21 + x2 = 0

Reorder the terms:
-21 + 15x + 6x2 + x2 = 0

Combine like terms: 6x2 + x2 = 7x2
-21 + 15x + 7x2 = 0

Solving
-21 + 15x + 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 + 2.142857143x + x2 = 0

Move the constant term to the right:

Add '3' to each side of the equation.
-3 + 2.142857143x + 3 + x2 = 0 + 3

Reorder the terms:
-3 + 3 + 2.142857143x + x2 = 0 + 3

Combine like terms: -3 + 3 = 0
0 + 2.142857143x + x2 = 0 + 3
2.142857143x + x2 = 0 + 3

Combine like terms: 0 + 3 = 3
2.142857143x + x2 = 3

The x term is 2.142857143x.  Take half its coefficient (1.071428572).
Square it (1.147959185) and add it to both sides.

Add '1.147959185' to each side of the equation.
2.142857143x + 1.147959185 + x2 = 3 + 1.147959185

Reorder the terms:
1.147959185 + 2.142857143x + x2 = 3 + 1.147959185

Combine like terms: 3 + 1.147959185 = 4.147959185
1.147959185 + 2.142857143x + x2 = 4.147959185

Factor a perfect square on the left side:
(x + 1.071428572)(x + 1.071428572) = 4.147959185

Calculate the square root of the right side: 2.036653919

Break this problem into two subproblems by setting 
(x + 1.071428572) equal to 2.036653919 and -2.036653919.

Subproblem 1

x + 1.071428572 = 2.036653919 Simplifying x + 1.071428572 = 2.036653919 Reorder the terms: 1.071428572 + x = 2.036653919 Solving 1.071428572 + x = 2.036653919 Solving for variable 'x'. Move all terms containing x to the left, all other terms to the right. Add '-1.071428572' to each side of the equation. 1.071428572 + -1.071428572 + x = 2.036653919 + -1.071428572 Combine like terms: 1.071428572 + -1.071428572 = 0.000000000 0.000000000 + x = 2.036653919 + -1.071428572 x = 2.036653919 + -1.071428572 Combine like terms: 2.036653919 + -1.071428572 = 0.965225347 x = 0.965225347 Simplifying x = 0.965225347

Subproblem 2

x + 1.071428572 = -2.036653919 Simplifying x + 1.071428572 = -2.036653919 Reorder the terms: 1.071428572 + x = -2.036653919 Solving 1.071428572 + x = -2.036653919 Solving for variable 'x'. Move all terms containing x to the left, all other terms to the right. Add '-1.071428572' to each side of the equation. 1.071428572 + -1.071428572 + x = -2.036653919 + -1.071428572 Combine like terms: 1.071428572 + -1.071428572 = 0.000000000 0.000000000 + x = -2.036653919 + -1.071428572 x = -2.036653919 + -1.071428572 Combine like terms: -2.036653919 + -1.071428572 = -3.108082491 x = -3.108082491 Simplifying x = -3.108082491

Solution

The solution to the problem is based on the solutions from the subproblems. x = {0.965225347, -3.108082491}

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