1.设s=1+1/2+1/4+…+1/2^n
=1*(1-(1/2)^(n+1))/(1-(1/2))
=2*(1-(1/2)^(n+1))
当n->无穷时,(1/2)^(n+1)=0
∴lims=2
2.原式=lim(1-1/x^2)/(x^2+3)(1+1/x^2)
=lim1/(x^2+3)
=0