Răspunsuri

2014-11-01T14:12:23+02:00
a=81+2*81+3*81+...+49*81 = 81(1+2+3+...+49)  \\ a= 81 \frac{49*50}{2}=81*49*25 \\ a= 9^{2}* 7^{2} * 5^{2}   =  315^{2} 


--> "a" este patrat perfect

Am folosit urmatoarea formula :
1+2+3+...+n =  \frac{n(n+1)}{2}
14 4 14