Question

aratati ca nr a=(3la21+3la20+3la19):39,este patrat perfect.

Answer 1

Uc = ultima cifra
1 +0 + 9 = Uc 0
.....0 ÷ la 9 = Uc 1
si un patrat perfect poate avea uc

Answer 2

(3^21+3^20+3^19):39=
=3^19(3^2+3^1+3^0):39=
=3^19 *(9+3+1):(3*13)=
=3^19 *13:(3*13)=
=3^19:3=3^18=(3^9)^2 deci patrat perfect