Ответ: [tex]P_4-2A_9^2+3C_8^2=4!-2* \frac{9!}{2!(9-2)!}+3* \frac{8!}{2!(8-2)!}=\\\\=4*3*2*1- \frac{2*9!}{2*7!}+ \frac{3*8!}{2*6!}=24-9*8+ \frac{3*8*7}{2}=\\\\=24-72+84=36 [/tex]