Question

find all the zeros of the polynomial x4-2x3-7x2+8x+12 whose two zeroes are -1 and2

Answer 1

In this question 2 zeroes are given, so two root of this polynomial is (x+1) and (x-2).
Now multiply these root and divide the polynomial equation:
(x4-2x3-7x2+8x+12)/(x2-x-2)
by solving this you can get another two roots which is x=1 and x=-2