Răspunsuri

2014-10-22T08:37:55+03:00
A=2003+2*(1+2+....+2002) =2003+2*2002*2003:2=2003+2002*2003=2003(1+2002)=2003*2003=2003²
aplicam formula 1+2+3+..+n=n*(n+1):2

b=1+3+5+.......+2011 =1+3+5+...+(2*1005+1)=(1005+1)²
aplicam formula 1+3+.5+...+(2n+1)=(n+1)²
a=81+2*81+3*81+.....+49*81=81*(1+2+3+...49)=81*49*50:2=81*49*25=9²*7²*5²=(9*7*5)²=315²
am demonstrat ca sunt patrate perfecte

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