x4−x3−2x−4=(x4−4)−(x3+2x)=(x2−2)(x2+2)−x(x2+2)=(x2+2)(x2−x−2)=(x+√2i)(x−√2i)(x−2)(x+1)
2) A fifth degree polynomial will have 5 complex zeros
3) x4+2x3−16x2−2x+15=(x4−16x2+15)+(2x3−2x)=(x2−15)(x2−1)+2x(x2−1)=(x2+2x−15)(x2−1)=(x−3)(x+5)(x−1)(x+1)and the zeros can be read off as x=3, −5, 1, −1
.