a,b属于(0,π/2)
a-π/6,b-π/6属于(-π/6,π/3)
sin(a-π/6)=3/5
cos(a-π/6)=4/5
sin(b-π/6)=12/13
cos(b-π/6)=5/13
所以
f(a-b)=sin[(a-π/6)-(b-π/6)]
=sin(a-π/6)cos(b-π/6)-cos(a-π/6)sin(b-π/6)
=3/5*5/13-4/5*12/13
=-13/45
a,b属于(0,π/2)
a-π/6,b-π/6属于(-π/6,π/3)
sin(a-π/6)=3/5
cos(a-π/6)=4/5
sin(b-π/6)=12/13
cos(b-π/6)=5/13
所以
f(a-b)=sin[(a-π/6)-(b-π/6)]
=sin(a-π/6)cos(b-π/6)-cos(a-π/6)sin(b-π/6)
=3/5*5/13-4/5*12/13
=-13/45