a) E(x)=(2x+1)²-(2x-1)²+(x-2)(x+2)-7x+5= 4x²+4x+1-4x²+4x-1+x²-4-7x+5= 4x²-4x²+x²+4x+4x-7x+1-1-4+5= x²+x+1
b) E(x)= x²+x+1=x²+x+1/4+1-1/4= [x²+2x*1/2+(1/2)²]+3/4=
=(x+1/2)²+3/4
(x+1/2)²>=0 pentru orice x€R
3/4>0
rezultă E(x)>0, pt orice x€R
