20.a)(215-15)(215+15)=200*230=46000
b)(196-96)(196+96)=100*292=29200
c)(1.5-0.5)(1.5+0.5)=1*2=2
d)(10.5-0.5)(10.5+0.5)=10*11=110
21.(x-y)(x+y)=4*6=24
(x-y)(x+y)=14; 7(x+y)=14; x+y=2
22.(a-b)(a+b)(a*a+b*b)
(a-1)(a+1)(a*a+1)
dupa principiul acesta le rezolvi pe toate
