C(5,r)(x-1/x)^(5-r)(-2)^rr=1(x-1/x)^4中的常数项为C(4,2)x²×(-1/x)²=6此时常数项=C(5,1)×6×（-2）=-602.r=3(x-1/x)^2中的常数项为C(2,1)x×(-1/x)=-2此时常数项=C(5,3)×(-2)×（-2）³=1603.r=5...