how to solve this kind of questions

hmm.. basicaly there is a good way to find the values of cos and sin of multiples of 6 degrees!

We do that by finding the multiple of 18 degrees!

for this problem u can convert cos 6 to sin 84

then apply the sum of sine rule

that will take it to a multiple of 18 degrees form.

Ditto for the second part!

I think u should look at how to find the sin and cos of multiple of 18 degrees....

But i think this will nto come in JEE. (I will check and let u know though!)

Btw i will look at the other questions u posted... (First look i had no solution to them :(