Suppose u⁽⁰⁾ = 1. Find u⁽¹⁾, u⁽¹⁰⁾, and u⁽²⁰⁾ when 

(a) u^(k+1) = 2u^(k),

(b) u^(k+1) = −.9u^(k),

(c) u^(k+1) = i u^(k),

(d) u^(k+1) = (1 − 2 i)u^(k)