1. 1)cos315=cos(360-45)=cos45=√2/2
2)sin 4p/3=sin(p+p/3)=-sin (p/3)=-√3/2
3)tg210=tg(180+30)=tg30=1/√3
2.sin=9/41
sin^2x+cos^2x=1
cosx=√1-81/1681√1600/1681=40/41
sin2x=2*cosx*sinx= 40/41*2*9/41=720/1640=36/82=18/41
3.sina*sinb-(cosa*cosb+sina*sinb)/cosa/sina=
-sin(a+b)-sin(a-b)/2