Question

n=(radical din 5 - 1 )totul la patrat + 2 radical din 5 este natural

Answer 1

$( \sqrt{5} -1)^{2}+2 \sqrt{5} = 5-2\sqrt{5}+1 +2 \sqrt{5}=6$ ∈N
Formula folosita
$(a-b)^{2} = a^{2}-2ab+ b^{2}$

Answer 2

$\displaystyle n=\left( \sqrt{5} -1 \right)^2+2 \sqrt{5} ~~~~~~~~~~~~~~~\boxed{(a-b)^2=a^2-2ab+b^2}\\ n=\left( \sqrt{5} \right)^2-2 \cdot \sqrt{5} \cdot 1+1^2+2 \sqrt{5} \\ n=5-2 \sqrt{5} +1+2 \sqrt{5} \\ n=6 \in N$