5) 1999+1999^2+2000
=1999(1+1999)+2000
=1999.2000+2000
=2000(1999+1)
=2000.2000=2000^2 ( 2000 la puterea 2) => este patrat perfect
6) m.A=2^2nx2x5^n+2^2nx2^2x5^nx5^2+5^nx2^nx2^nx3
=2^2nx2x5^n+2^2nx2^2x5^nx5^2+5^nx2^2nx3
=2^nx5^n(2+2^2x5^2+3)
=2^nx5^n(2+4x25+3)
=2^nx5^nx105
105 este divizibil cu 7, => 2^nx5Nx104:7
