Question

sec² 10°- cot² 80° = ?

(a) 1 

(b) 0 

(c) 3/2 

(d) 1/2

Answer 1

Correct answer = (a) 1

We have: 

(sin 79° cos 11° + cos 79° sin 11°) 

= sin 79° cos(90° − 79° ) + cos 79° sin(90° − 79°)

= sin 79° sin 79° + cos 79° cos 79° [∵ cos(90° − θ) = sin θ and sin(90° − θ) = cos θ] 

= sin² 79° + cos² 79° 

= 1