a=√11+4√7
x²+y²=11
2xy=4√7
xy=2√7
Observam ca daca x=2 si y=√7, x²+y²=4+7=11
a=√(2+√7)²=|2+√7|
Cum 2+√7>0 => a=2+√7
b=√11-4√7
x²+y²=11
-2xy=4√7
-xy=2√7
Observam ca daca x=-2 si y=√7, x²+y²=4+7=11
b=√(2-√7)²=|2-√7|
Cum 2-√7<0 => b=√7-2
a*b=(2+√7)(2-√7)=4-7=-3
(a-b)²=16a-b=2+√7-(√7-2)=2+√7-√7+2=4(a-b)²=4²=16
