Răspuns:
1.r= a3-a2= 5-3= 2
a1= a2-r= 3-2=1
2. f(n)=3
n^2-1=3
n^2= 4-----> n=+/- 2
f(2)=2^2-1= 4-1= 3 (A)
3.x^2-9= (x+3)^2
Dacă ridicăm tot la pătrat se obține: x^2-9= x^2-2x+1
-2x= -10------> x= 5
Verificare: 5^2-9= 5^2-2×5+1---->
---->16= 16
4. {1,2,3,4}
( 1,2,3), (2,3,4), (1,2,4), (1,3,4) -deci 4.
Succes!
