Question

已知ab均为锐角,若cosa=4/5,cos(a+b)=5/13,则sinb=

Answer 1

ab均为锐角,cosa=4/5,cos(a+b)=5/13,则

sina=3/5,sin(a+b)=12/13

sinb

=sin[(a+b)-a]

=sin(a+b)*cosa-cos(a+b)*sina

=12/13*4/5-5/13*3/5

=48/65-15/65

=33/65