Question

cos72度*cos36度等于多少？

Answer 1

2sin36°cos36°=sin(2*36°)=sin72°=sin(180°-72°)=sin108°=sin(3*36°)=3sin36°-4sin�0�636°=sin36°(3-4sin�0�536°)=sin36°[3-4(1-cos�0�536°)]=sin36°(4cos�0�536°-1)4cos�0�536°-2cos36°-1=0,cos36°=[2+√(2�0�5+4*4*1)]/(2*4)=(√5+1)/4cos72°cos36°=cos(2*36°)cos36°=(2cos�0�536°-1)cos36°={2[(√5+1)/4]�0�5-1}(√5+1)/4=(3-√5)/2

Answer 2

0.25

Answer 3

cos72°cos36°
=2sina36°cos72°cos36°/2sina36°
=sin72°cos72°/2sin36°
=2sin72°cos72°/4sin36°
=sin144°/4sin36°
=sin36°/4sin36°
=1/4