Question

mojete pojalosto reshit ya nekak ne magu ponyat kak reshat faktariali​

Answer 1

$C^2_9=\dfrac{9!}{2!*(9-2)!}=\dfrac{1*2*3*4*...*8*9}{2*1*2*3*4*...*6*7}=\\\\\\=\dfrac{8*9}{2}=4*9=36$