sina/2-cosa/2=根5/5（a大于二分之派小于派）求sin asin(a/2)

sina/2-cosa/2=根5/5（a大于二分之派小于派）求sin asin(a/2)
sina/2-cosa/2=根5/5（a大于二分之派小于派）求sin a
sin(a/2)

sina/2-cosa/2=根5/5（a大于二分之派小于派）求sin asin(a/2)
是（sina）/2还是sin（a/2）
[sin(a/2)-cos(a/2)]^2=1/5
1-sin a=1/5
sin a=4/5

[sin(a/2)-cos(a/2)]^2=(根5/5)^2
[sin(a/2)]^2+[cos(a/2)]^2-2sin(a/2)*cos(a/2)=1/5
1-sin a=1/5
sin a=4/5