f(x)=sqrt(360/x)*sin(x)
=(360)^(1/2)*x^(-1/2)* sin x
f'(x)=(360)^(1/2)*[(-1/2)*x^(-3/2)*sin x + x^(-1/2)*cos x]
=(360)^(1/2)*x^(-1/2)*[(-1/2)*x^(-1)*sin x + cos x]
f'(x)=0 時有最大值, (-1/2)*x^(-1)*sin x + cos x = 0
tan x - 2x = 0 ---> x ~ 66.78 度 (x要以弳度表示)