Question

Ajutati-ma la aranjamente si combinari ex 12

Answer 1

$A^2_{n}=42;DVA:n \geq 2 \\ \frac{n!}{(n-2)!}=42 \\ \frac{(n-2)!(n-1)n}{(n-2)!} =42 \\ n^2-n-42=0$
Δ=169
$n_{1}= \frac{1-13}{2}=-6 \\ n_{2}= \frac{1+13}{2}=7$
$C^3_{n}=6n;DVA:n \geq 3 \\ \frac{n!}{3!(n-3)!}=6n \\ \frac{(n-3)!(n-2)(n-1)n}{6(n-3)!} =6n \\ (n-2)(n-1)n=36n \\ (n-2)(n-1)n-36n=0 \\ n[(n-2)(n-1)-36)=0 \\ n=0 sau n^2-3n-34=0$
Δ=9+136=145
S=∅