化简sin18*cos36

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化简sin18*cos36化简sin18*cos36化简sin18*cos36sin18*cos36=sin18*cos36*sin72/sin72=sin18*cos36*sin72/sin72=s

化简sin18*cos36
化简sin18*cos36

化简sin18*cos36
sin18*cos36=sin18*cos36*sin72/sin72
=sin18*cos36*sin72/sin72
=sin18*cos36*cos18/sin72
=(sin18*cos18)*cos36/sin72
=(1/2sin36)*cos36/sin72
=1/4sin72/sin72
=1/4

乘以4cos18,再除以4cos18
4cos18*sin18*cos36/(4cos18)=2sin36*cos36/(4cos18)=sin72/(4cos18)=cos18/(4cos18)=1/4

sin18*cos36=sin18*cos18*cos36/cos18
=sin36*cos36/2cos18=sing72/4cos18=cos18/4cos18=1/4

sin18*cos36
=2sin18*cos18*cos36/(2cos18 )
=sin36*cos36/(2cos18)
=sing72/(4cos18)
=cos18/(4cos18)
=1/4