$(2+x+\frac{5}{x})^7=\sum^7_{k=0}C^k_72^{7-k}(x+\frac{5}{x})^k=\sum^7_{k=0}C^k_72^{7-k}\sum^k_{l=0}C^l_kx^{k-l}\frac{5^l}{x^l}$$=\sum^7_{k=0}\sum^k_{l=0}C^k_7C^l_k2^{7-k}.5^l.x^{k-2l}$$\Rightarrow T_{k+1}=C^k_7C^l_k2^{7-k}5^lx^{k-2l}$
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28-03-14 04:21 AM
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