Prove that
(a-1 + b-1)-1 = ab/a+b
cotA+sinA÷cotA-sinA=1-cosA+secA÷1+cosA-secA
Prove that:
(i) a+b+ca−1b−1+b−1c−1+c−1a−1=abc
(ii) (a−1+b−1)−1=aba+b