9 sec2 A − 9 tan2 A is equal to
To find: 9 sec2 A – 9 tan2 A
Consider 9 sec2 A – 9 tan2 A = 9 (sec2 A – tan2 A)
∵ 1 + tan2 A = sec2 A
∴ 9 sec2 A – 9 tan2 A = 9 (sec2 A – tan2 A)
= 9 (1 + tan2 A – tan2 A) = 9