Answer:
(y -5)(y -i√6)(y +i√6)
Explanation:
The expression can be factored by grouping:
(y^3 -5y^2) +(6y -30) = y^2(y -5) +6(y -5) = (y^2 +6)(y -5)
The quadratic factor is the difference of squares, if you consider -6 to be a square. In that view, it can be factored as ...
y^2 +6 = (y -i√6)(y +i√6)
Then the complete factorization is ...
(y -5)(y -i√6)(y +i√6)