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 cos (u;v)=( u. v)/(uv) sin (u;v)=Det ( u; v)/(uv) ( u. v)=xx'+yy' Det ( u; v)=xy'-yx'
 cos ( /2-x)=sin x sin ( /2-x)=cos x cos ( +x)=-cos x sin ( +x)=-sin x
 cos (a+b)=cos acos b-sin asin b cos (a-b)=cos acos b+sin asin b sin (a+b)=sin acos b+sin bcos a sin (a-b)=sin acos b-sin bcos a cos 2a=cos Za-sin Za=2cos Za-1=1-2sin Za sin 2a=2sin acos a cos Za=(1+cos 2a)/2 sin Za=(1-cos 2a)/2
 x cos X=cos   X= +2k  X=- +2k  x sin X=sin   X= +2k  X= - +2k 

+ CHANGE LE SGN
 2- CHG cos EN sin ET sin EN cos 
 x cos (X+Y)=cos Xxcos Y-sin Xxsin Y x cos (X-Y)=cos Xxcos Y+sin Xxsin Y x sin (X+Y)=sin Xxsin Y+cos Xxsin Y x sin (X-Y)=sin Xxcos Y-cos Xxsin Y x cos 2X=cos ZX-sin ZX=2cos ZX-1=1-2sin ZX 1 sin 2X=2sin Xxcos X x cos ZX=(1+cos 2X)/2 x sin ZX=(1-cos 2X)/2 x LIM(H 0) sin H/H=1
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