sina=1/3 cosa=-2√2/3
cosb=-1/4 sinb=-√15/4
cos(a-b)
=cosacosb+sinasinb
=2√2/12-√15/12
sin(a+b)
=sinacosb+cosasinb
=-1/12-2√30/12
cos2a=1-2sin^2a=1-2/9=7/9
=
sina=1/3 cosa=-2√2/3
cosb=-1/4 sinb=-√15/4
cos(a-b)
=cosacosb+sinasinb
=2√2/12-√15/12
sin(a+b)
=sinacosb+cosasinb
=-1/12-2√30/12
cos2a=1-2sin^2a=1-2/9=7/9
=