Question

Describe and correct the error.

Solve x^3 + 20x= -2x^3 - 7x
3x^3 + 27x = 0
3x(x^2 + 9) = 0
3x(x-3)(x + 3) = 0
x = { -3, 0, 3}

Answer 1

Explanation:

x² + 9 doesn't factor into (x − 3) (x + 3). That's the factorization for the difference of squares, not a sum of squares.

x² + 9 has only imaginary factors: (x − 3i) (x + 3i).

x = {-3i, 0, 3i}

If x is only real numbers, then x = {0}