[tex](a+b)^2=1\\
a^2+2ab+b^2=1\\
a^2+b^2=1-2ab\\
a^4+b^4+2a^2b^2=1-4ab+4a^2b^2\\
a^4+b^4+1=2-4ab+2a^2b^2=2(1-2ab+a^2b^2)=2(ab-1)^2\\
e_{(a,b)}=\frac{2(ab-1)^2}{(ab-1)^2}=2\\
2)
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La ex 3 e o greseala ! [tex]A=\{x\in R|x^3-2x^2-x+2=0}\}\\
x^2(x-2)-(x-2)=(x-2)(x^2-1)=(x-2)(x-1)(x+1)=0\\
x-2=0\\x_1=2\\
x-1=0\\
x_2=1\\
x+1=0\\
x_3=-1\\
A=\{2,1,-1\}\\
[/tex]
A∩{1,2,3}={1,2}, deci raspunsul corect este c) 2
