cost-1=-2[sin(t/2)]^2=2[sin(t/2)]^(1/3)*[sin(t/2)]^(5/3)
所以原式={2[sin(t/2)]^(1/3)*[sin(t/2)]^(5/3)}/[8*(t/2)^(1/3)]
令t/2=x
原式={2sinx^(1/3)*sinx^(5/3)}/[8*x^(1/3)]
=(1/4)*[(sinx)/x]^(1/3)*sinx^(5/3)
(sinx)/x在0处的极限为1
sinx^(5/3)在0处的极限为0
原极限=(1/4)*1*0=0
所以极限值为0