(2x-x^(-1/2))^6 展开项为 C(i,6)(2x)^(6-i) *(x^(-1/2))^(i) =C(i,6)2^(6-i) x^(6-3i/2) i=4,展开项为常数项 C(4,6)2^2 =15*4 =60 C(m,n)是n个数中找个m个的组合数
