sin 47 =sin(30+17)=sin30cos17+sin17cos30
sin47-sin17*cos30/cos17
=(sin30cos17+sin17cos30-sin17*cos30)/cos17
=sin30cos17/cos17
=sin30
=1/2
sin 47 =sin(30+17)=sin30cos17+sin17cos30
sin47-sin17*cos30/cos17
=(sin30cos17+sin17cos30-sin17*cos30)/cos17
=sin30cos17/cos17
=sin30
=1/2