f(1)=1+p+q
f(2)=4+2p+q
f(3)=9+3p+q
假设命题不成立,则同时有:
|1+p+q|=|A-B|,可推广到多个数)
而由(1)(2)(3)式有:|1+p+q|+2|4+2p+q|+|9+3p+q|