(1+tan A)2+(1−tan A)2=
2
1
2 sec2 A
2 cos2 A
⇒(1+tanA)2+(1−tanA)2 =(1+tan2A+2tanA)+(1+tan2A−2tanA) =(2+2tan2A+2tanA−2tanA) =(2+2tan2A) =2(1+tan2A) =2sec2A
Cosec A+1/ cosec A- 1 = (sec A+ tan A)2