21+3x=x(-5x+4)

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Solution for 21+3x=x(-5x+4) equation:


Simplifying
21 + 3x = x(-5x + 4)

Reorder the terms:
21 + 3x = x(4 + -5x)
21 + 3x = (4 * x + -5x * x)
21 + 3x = (4x + -5x2)

Solving
21 + 3x = 4x + -5x2

Solving for variable 'x'.

Combine like terms: 3x + -4x = -1x
21 + -1x + 5x2 = 4x + -5x2 + -4x + 5x2

Reorder the terms:
21 + -1x + 5x2 = 4x + -4x + -5x2 + 5x2

Combine like terms: 4x + -4x = 0
21 + -1x + 5x2 = 0 + -5x2 + 5x2
21 + -1x + 5x2 = -5x2 + 5x2

Combine like terms: -5x2 + 5x2 = 0
21 + -1x + 5x2 = 0

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

Divide each side by '5'.
4.2 + -0.2x + x2 = 0

Move the constant term to the right:

Add '-4.2' to each side of the equation.
4.2 + -0.2x + -4.2 + x2 = 0 + -4.2

Reorder the terms:
4.2 + -4.2 + -0.2x + x2 = 0 + -4.2

Combine like terms: 4.2 + -4.2 = 0.0
0.0 + -0.2x + x2 = 0 + -4.2
-0.2x + x2 = 0 + -4.2

Combine like terms: 0 + -4.2 = -4.2
-0.2x + x2 = -4.2

The x term is -0.2x.  Take half its coefficient (-0.1).
Square it (0.01) and add it to both sides.

Add '0.01' to each side of the equation.
-0.2x + 0.01 + x2 = -4.2 + 0.01

Reorder the terms:
0.01 + -0.2x + x2 = -4.2 + 0.01

Combine like terms: -4.2 + 0.01 = -4.19
0.01 + -0.2x + x2 = -4.19

Factor a perfect square on the left side:
(x + -0.1)(x + -0.1) = -4.19

Can't calculate square root of the right side.

The solution to this equation could not be determined.

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