Question

evaluate (without using table) : b) cos13°×cosec77°​

Answer 1

So we know,

Sin A = cos (90-A)

so in cos 13 we can write it as sin (90-13)

= sin 77

and cosec A = 1/ sin a

So

cos 13 × cosec 77

= sin 77 × 1/sin 77

= 1

So , cos13°×cosec77° = 1