Use a sum or difference formula to find the exact value of the following.

Question

sin2∏/5 cos3∏/20 + cos3∏/5 sin3∏/20

 

 

Answer 1

Muhaman,

 

This is another example of where you can apply the suggestions given to you by Kenneth in your posting on how to simplify expressions like 2sin35°cos35°.  Andy applied the identity for sin(x ± y).

Answer 2

It looks like you mistyped the second to the last term.

Perhaps it should read cos 2pi/5

 

IF so, then it is sin(2pi/5 + 3pi/20) = sin(11pi/20) = sin(99) = 0.987688.....