已知数列{an}的通项公式是an=(2^n-1)/2^n,其实前n项和Sn=321/64,项数n=an=((2^n)-1)/2^n=1-(1/2^n)Sn = a1+..+an=1-1/2+1-1/4+...+1-1/2^n=n-(1/2+1/4+...+1/2^n)=n-(0.5-0.5*0.5^n)/(1-0.5)=n-1+0.5^n=321/64n-1+0.5^n=321/64我想问问这样
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![已知数列{an}的通项公式是an=(2^n-1)/2^n,其实前n项和Sn=321/64,项数n=an=((2^n)-1)/2^n=1-(1/2^n)Sn = a1+..+an=1-1/2+1-1/4+...+1-1/2^n=n-(1/2+1/4+...+1/2^n)=n-(0.5-0.5*0.5^n)/(1-0.5)=n-1+0.5^n=321/64n-1+0.5^n=321/64我想问问这样](/uploads/image/z/1102243-67-3.jpg?t=%E5%B7%B2%E7%9F%A5%E6%95%B0%E5%88%97%7Ban%7D%E7%9A%84%E9%80%9A%E9%A1%B9%E5%85%AC%E5%BC%8F%E6%98%AFan%3D%EF%BC%882%5En-1%EF%BC%89%2F2%5En%2C%E5%85%B6%E5%AE%9E%E5%89%8Dn%E9%A1%B9%E5%92%8CSn%3D321%2F64%2C%E9%A1%B9%E6%95%B0n%3Dan%3D%28%282%5En%29-1%29%2F2%5En%3D1-%281%2F2%5En%29Sn+%3D+a1%2B..%2Ban%3D1-1%2F2%2B1-1%2F4%2B...%2B1-1%2F2%5En%3Dn-%281%2F2%2B1%2F4%2B...%2B1%2F2%5En%29%3Dn-%280.5-0.5%2A0.5%5En%29%2F%281-0.5%29%3Dn-1%2B0.5%5En%3D321%2F64n-1%2B0.5%5En%3D321%2F64%E6%88%91%E6%83%B3%E9%97%AE%E9%97%AE%E8%BF%99%E6%A0%B7)
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