Question

Can someone solve this equation. I will mark you the BRAINLIEST!

$x^{3} - 21x - 90 = 0$

Answer 1

Answer:

${x}^{3} - 21x - 90 = 0$

${x}^{3} - 36x + 15x - 90 = 0$

$x( {x}^{2} - 36) + 15(x - 6) = 0$

$x \times (x - 6) \times ( x+ 6) + 15(x - 6) = 0$

$(x - 6) \times (x \times (x + 6) + 15) = 0$

$(x - 6) \times ( {x}^{2} + 6x + 15) = 0$

X - 6 = 0

X = 6

${x}^{2} + 6x + 15 = 0$

X € R

Therefore, x = 6