若p,q是实数,p³+q³=2 求0＜p+q≤2 急

2=p^3+q^3=(p+q)(p^2+q^2-pq)=(p+q)[(p+q)^2-3pq]
>= (p+q)[(p+q)^2-3/4(p+q)^2]
=(p+q)[1/4 (p+q)^2]
=1/4*(p+q)^3
(p+q)^30,则有p+q>0
所以,0＜p+q≤2