1/2+1/4+1/8+1/16+ +1/2n=?
问题描述：
1/2+1/4+1/8+1/16+ +1/2n=?
答
=1-1/2+1/2-1/4+1/4-1/8+……+1/(2n-2)-1/2n
=1-1/2n
答
这是以1/2为首项 1/2为公比的等比数列，直接代入前n项和公式即可，值为1-1/2^n
答
应该是1/2+1/4+1/8+1/16+......+1/2^n=?
1/2+1/4+1/8+1/16+......+1/2^n
=1/2+1/4+1/8+1/16+......+1/2^(n-1)+[1/2^n+1/2^n]-1/2^n
=1/2+1/4+1/8+1/16+......+1/2^(n-1)+1/2^(n-1)-1/2^n
......
=1/2+1/4+1/8+1/16+1/16-1/2^n
=1/2+1/4+1/8+1/8-1/2^n
=1/2+1/4+1/4-1/2^n
=1/2+1/2-1/2^n
=1-1/2^n
答
1-1/(2n)
为什么限制字数不能太少.....
答
1/2+1/4+1/8+1/16+ +1/2n
=（1/2-1/2n*1/2）/(1-1/2)
=1-1/2n
等比数列求和公式记住即可!
a1=1/2,an=1/2n,q=1/2