sin（x+y）sin(x-y)=sin^2x-sin^2y是证明题,写下过程哦,嘿嘿我有点看不懂~~~~~~5555555555

Question

sin（x+y）sin(x-y)=sin^2x-sin^2y
是证明题,写下过程哦,嘿嘿
我有点看不懂~~~~~~5555555555

Answer 1

本题应用积化和差公式：（先说说公式推导：cos（x+y)=cosxcosy-sinxsiny;cos(x-y)=cosxcosy+sinxsiny;于是sinxsiny=(cos(x-y)-cos(x+y))/2;)将公式应用于本题左边=sin（x+y）sin(x-y)=(cos2y-cos2x)/2=(1-2sin^2y-1+...