Sn=(2/3)的0次方×1+(2/3)的1次方×3+(2/3)的2次方×5……+(2/3)的(n-1)次方×(2n-1) 求Sn.怎么算,请各Sn=(2/3)的0次方×1+(2/3)的1次方×3+(2/3)的2次方×5……+(2/3)的(n-1)次方×(2n-1)求Sn。(n是自然数) 怎么算,
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![Sn=(2/3)的0次方×1+(2/3)的1次方×3+(2/3)的2次方×5……+(2/3)的(n-1)次方×(2n-1) 求Sn.怎么算,请各Sn=(2/3)的0次方×1+(2/3)的1次方×3+(2/3)的2次方×5……+(2/3)的(n-1)次方×(2n-1)求Sn。(n是自然数) 怎么算,](/uploads/image/z/8875471-31-1.jpg?t=Sn%3D%282%2F3%29%E7%9A%840%E6%AC%A1%E6%96%B9%C3%971%2B%282%2F3%29%E7%9A%841%E6%AC%A1%E6%96%B9%C3%973%2B%282%2F3%29%E7%9A%842%E6%AC%A1%E6%96%B9%C3%975%E2%80%A6%E2%80%A6%2B%282%2F3%29%E7%9A%84%28n-1%29%E6%AC%A1%E6%96%B9%C3%97%282n-1%29+%E6%B1%82Sn.%E6%80%8E%E4%B9%88%E7%AE%97%2C%E8%AF%B7%E5%90%84Sn%3D%282%2F3%29%E7%9A%840%E6%AC%A1%E6%96%B9%C3%971%2B%282%2F3%29%E7%9A%841%E6%AC%A1%E6%96%B9%C3%973%2B%282%2F3%29%E7%9A%842%E6%AC%A1%E6%96%B9%C3%975%E2%80%A6%E2%80%A6%2B%282%2F3%29%E7%9A%84%28n-1%29%E6%AC%A1%E6%96%B9%C3%97%282n-1%29%E6%B1%82Sn%E3%80%82%EF%BC%88n%E6%98%AF%E8%87%AA%E7%84%B6%E6%95%B0%EF%BC%89+%E6%80%8E%E4%B9%88%E7%AE%97%EF%BC%8C)
Sn=(2/3)的0次方×1+(2/3)的1次方×3+(2/3)的2次方×5……+(2/3)的(n-1)次方×(2n-1) 求Sn.怎么算,请各Sn=(2/3)的0次方×1+(2/3)的1次方×3+(2/3)的2次方×5……+(2/3)的(n-1)次方×(2n-1)求Sn。(n是自然数) 怎么算,
Sn=(2/3)的0次方×1+(2/3)的1次方×3+(2/3)的2次方×5……+(2/3)的(n-1)次方×(2n-1) 求Sn.怎么算,请各
Sn=(2/3)的0次方×1+(2/3)的1次方×3+(2/3)的2次方×5……+(2/3)的(n-1)次方×(2n-1)
求Sn。(n是自然数) 怎么算,算了好久算不出来,好难过……
Sn=(2/3)的0次方×1+(2/3)的1次方×3+(2/3)的2次方×5……+(2/3)的(n-1)次方×(2n-1) 求Sn.怎么算,请各Sn=(2/3)的0次方×1+(2/3)的1次方×3+(2/3)的2次方×5……+(2/3)的(n-1)次方×(2n-1)求Sn。(n是自然数) 怎么算,
这是复合型的数列,即一个等差数列乘以一个等比数列.通常的做法就是错位相减法.
即将Sn乘以等比数列的公比.
Sn×2/3=(2/3)的1次方×1+(2/3)的2次方×3+.+(2/3)的n-1次方×(2n-3)+(2/3)的n次方×(2n-1)
两者做差.
Sn×1/3=1+2×(2/3)+2×(2/3)的2次方+2×(2/3)的三次方+.+2×(2/3)的n-1次方-(2/3)的n次方乘以2n-1
做差后是个等比数列和一项n的式子,就可以把最终的结果求出来了.
要结果还是要过程?
要用错位相减的方法