Question

решите уравнение по теме: Бином Ньютона
5*C^3_n=C^4_n+2

Answer 1

$\displaystyle 5C_n^3=C_{n+2}^4\\\\5* \frac{n!}{3!(n-3)!}= \frac{(n+2)!}{4!(n+2-4)!}\\\\5 \frac{n!}{3!(n-3)!}= \frac{n!(n+1)(n+2)}{3!*4*(n-3)!(n-2)}\\\\ 5\frac{1}{1}= \frac{(n+1)(n+2)}{4(n-2)}\\\\20(n-2)=(n+1)(n+2)\\\\20n-40=n^2+3n+2\\\\n^2-17n+42=0\\\\D=289-168=121=11^2\\\\n_1=3; n_2=14$