is there any formula or neat trick to factorise a cubic equation like
x^3 + 4x^2 -28x + 32=0?
Yes, use the factor and remainder theorems.
For any polynomial $\displaystyle P(x)$, if $\displaystyle P(a) = 0$ then $\displaystyle x - a$ is a factor.
The factors of $\displaystyle 32$ are $\displaystyle \pm 1, \pm 2, \pm 4, \pm 8, \pm 16, \pm 32$.
So try substituting these values into the expression.