B
bongtuyet96


CMR:
[latex]C_{n}^k+4C_{n}^{k-1}+C_{n}^{k-2}+4C_{n}^{k-3}+C_{n}^{k-4}=C_{n+4}^k[/latex]
[latex]C_{n}^1+2.\frac{C_{n}^2}{C_{n}^1}+3.\frac{C_{n}^3}{C_{n}^2}+...+n.\frac{C_{n}^n}{C_{n}^{n-1}}=C_{n+1}^2[/latex]
bài 2: tìm n biết
[latex]C_{n+1}^2+2.C_{n+2}^2+2.C_{n+3}^2+C_{n+4}^2=149[/latex]
mình cần gấp hehehe........thank các bạn trc'...
[latex]C_{n}^k+4C_{n}^{k-1}+C_{n}^{k-2}+4C_{n}^{k-3}+C_{n}^{k-4}=C_{n+4}^k[/latex]
[latex]C_{n}^1+2.\frac{C_{n}^2}{C_{n}^1}+3.\frac{C_{n}^3}{C_{n}^2}+...+n.\frac{C_{n}^n}{C_{n}^{n-1}}=C_{n+1}^2[/latex]
bài 2: tìm n biết
[latex]C_{n+1}^2+2.C_{n+2}^2+2.C_{n+3}^2+C_{n+4}^2=149[/latex]
mình cần gấp hehehe........thank các bạn trc'...
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