5.
a) E(n) = n^2+n+1
Pt. n =par => n=2k => E(n)=4k^2+2k+1 =2(2K^2 +k) +1 = impar
Pt. n=impar => n = 2k+1 => E(n)= 4k^2+4k+1+2k+1+1 =
= 4k^2 + 4k +2 +1 = 2( 2k^2+2k+1) + 1 = impar
b) rad(x^2+x+1) >= rad3/2 => ridicam la patrat
x^2+x+1 >= 3/4
4x^2 + 4x +4 >=3
4x^2 + 4x +1 >=0
(2x+1)^2 >= 0 evident
