Question

Solve `cos(-60^o)-tan135^o-:tan315^o +cos660^o`?

Answer 1

`cos(-60^o)-tan135^o-:tan315^o +cos660^o=0`

Explanation:

To solve `cos(-60^o)-tan135^o-:tan315^o +cos660^o`

we make use of `cos60^o=1/2` and `tan45^o=1` and also the identities `cos(-A)=cosA` and `tan(360^o-A)=tan(180^o-A)=-tanA`.

Hence `cos(-60^o)-tan135^o-:tan315^o +cos660^o`

= `cos60^o-tan(180^o-45^o)-:tan(360^o-45^o) +cos(720^o-60^o)`

= `cos60^o-(-tan45^o)-:(-tan45^o) +cos(-60^o)`

= `1/2-(-1)-:(-1) +cos60^o`

= `1/2-1+1/2=0`