Question

Question #5b0ed

Answer 1

`cos(arctan(2/3)`

let `arctan(2/3)=theta`

`=>tantheta=2/3`

`=>tan^2theta=(2/3)^2=4/9`

`=>1+tan^2theta=1+4/9`

`=>sec^2theta=13/9`

`=>cos^2theta=9/13`

`=>costheta=3/sqrt13`

`=>cos(arctan(2/3))=3/sqrt13`