you know, if you check your calculator, it has a [ ₙPᵣ ] and also an [ ₙCᵣ ] button, and you could use that, now, if you want the factorial version,
[tex]\bf _nP_r=\cfrac{n!}{(n-r)!}\qquad \qquad \qquad \qquad _nC_r=\cfrac{n!}{r!(n-r)!}
\\\\\\
_9P_3=\cfrac{9!}{(9-3)!}\qquad \qquad \qquad \qquad _9C_6=\cfrac{9!}{6!(9-6)!}[/tex]
