x=1002+2(1+2+...1001)=1002+2*1001*1002/2=1002+1001*1002=1002(1+1001)=1002*1002=1002²;;;la b si c ai o suma de nr impare consecutive care intotdeauna este egala cu nr de termeni la patrat. => (307+1)/2=308/2=158 termeni => x=158². la c) nr de termeni =(403+1)/2=404/2=202 => x=202²;;; d)x=4(1+2+...49=4*49*50/2=2*49*50=4900=70²
