F(x)=∫f(x)dx│(from x=-∞ to x)
F(x)=0 x=1
P{X＞a}=1-F(a)=1-a³=0.784
a³=0.216
a=0.6x≥1的情况不用考虑吗x>=1时 F(x)=1,P{X＞x}=1-F(x)=0<0.784不用考虑