Simplify (1+i / 1-i) + (1 -i/1+i)

Land is to arable ; river is a, navigable b, shallow c, presumsor d, water

What is the meaning of the prefix un-? a. over b. above c. under d. not

A(t)=(t−k)(t−3)(t−6)(t+3) is a polynomial function of tt, where kk is a constant. given that a(2)=0a(2)=0, what is the absolute value of the product of the zeros of aa?