4x^2-21=-3x

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Solution for 4x^2-21=-3x equation:


Simplifying
4x2 + -21 = -3x

Reorder the terms:
-21 + 4x2 = -3x

Solving
-21 + 4x2 = -3x

Solving for variable 'x'.

Reorder the terms:
-21 + 3x + 4x2 = -3x + 3x

Combine like terms: -3x + 3x = 0
-21 + 3x + 4x2 = 0

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

Divide each side by '4'.
-5.25 + 0.75x + x2 = 0

Move the constant term to the right:

Add '5.25' to each side of the equation.
-5.25 + 0.75x + 5.25 + x2 = 0 + 5.25

Reorder the terms:
-5.25 + 5.25 + 0.75x + x2 = 0 + 5.25

Combine like terms: -5.25 + 5.25 = 0.00
0.00 + 0.75x + x2 = 0 + 5.25
0.75x + x2 = 0 + 5.25

Combine like terms: 0 + 5.25 = 5.25
0.75x + x2 = 5.25

The x term is 0.75x.  Take half its coefficient (0.375).
Square it (0.140625) and add it to both sides.

Add '0.140625' to each side of the equation.
0.75x + 0.140625 + x2 = 5.25 + 0.140625

Reorder the terms:
0.140625 + 0.75x + x2 = 5.25 + 0.140625

Combine like terms: 5.25 + 0.140625 = 5.390625
0.140625 + 0.75x + x2 = 5.390625

Factor a perfect square on the left side:
(x + 0.375)(x + 0.375) = 5.390625

Calculate the square root of the right side: 2.321771953

Break this problem into two subproblems by setting 
(x + 0.375) equal to 2.321771953 and -2.321771953.

Subproblem 1

x + 0.375 = 2.321771953 Simplifying x + 0.375 = 2.321771953 Reorder the terms: 0.375 + x = 2.321771953 Solving 0.375 + x = 2.321771953 Solving for variable 'x'. Move all terms containing x to the left, all other terms to the right. Add '-0.375' to each side of the equation. 0.375 + -0.375 + x = 2.321771953 + -0.375 Combine like terms: 0.375 + -0.375 = 0.000 0.000 + x = 2.321771953 + -0.375 x = 2.321771953 + -0.375 Combine like terms: 2.321771953 + -0.375 = 1.946771953 x = 1.946771953 Simplifying x = 1.946771953

Subproblem 2

x + 0.375 = -2.321771953 Simplifying x + 0.375 = -2.321771953 Reorder the terms: 0.375 + x = -2.321771953 Solving 0.375 + x = -2.321771953 Solving for variable 'x'. Move all terms containing x to the left, all other terms to the right. Add '-0.375' to each side of the equation. 0.375 + -0.375 + x = -2.321771953 + -0.375 Combine like terms: 0.375 + -0.375 = 0.000 0.000 + x = -2.321771953 + -0.375 x = -2.321771953 + -0.375 Combine like terms: -2.321771953 + -0.375 = -2.696771953 x = -2.696771953 Simplifying x = -2.696771953

Solution

The solution to the problem is based on the solutions from the subproblems. x = {1.946771953, -2.696771953}

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