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2
cosa-cosb--2sin(a-b)/2*sin(a+b)/2
cos75-cos55=-2sin10*sin65

sina+sinb=2sin(a+b)/2*cos(a-b)/2
sin15+sin105=2sin60*cos45=2*√3/2*√2/2=√9/2

cosa+cosb=2cos(a-b)/2*cos(a+b)/2
cos121+cos59=2cos31*cos90=2cos31*0=0
3
cosa*sinb=1/2*(sin(a-b)+sin(a+b))
cos16*sin14=1/2*(sin2+sin30)=1/2*(sin2+1/2)=1/2*sin2+1/4

cosa*cosb=1/2*(cos(a-b)+cos(a+b))
cos(71*cos11=1/2*(cos60+cos82)=1/2(1/2+cos82)=1/4+1/2*cos82

sina*sinb=1/2*(cos(a-b)-cos(a+b))
sin46*sin14=1/2*(cos32-cos60)=1/2*(cos32-1/2=1/2*cos32-1/4
4
sinacosb-cosasinb=sin(a-b)
sin100cos10-cos100sin10=sin(100-10)=sin90=1

sin95cos5+cos35sin65=1/2*(sin100+sin90)+1/2(sin30+sin100)=
=1/2*sin100+1/2*1+1/2*1/2+1/2*sin100=sin100+3/4=cos10+3/4