A) Prove thatC* is a group under multiplication

B) let H={a+bi€ G|a^2 + b^2 = 1}. Prove that H is a subgroup ofC*.

C) Prove that the set ofnth roots of unity Unis a subgroup of H

D) let G be the group of all real 2x2 matrices of the form (a,b, -b, a, where not bothaandbare 0, under matrix multiplication. Show thatC* and G are isomorphic.