观察下面三行数:2,-4,8,-16,32,-64,…; ①4,-2,10,-14,34,-62,…;②1,-
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观察下面三行数:
2,-4,8,-16,32,-64,…; ①
4,-2,10,-14,34,-62,…;②
1,-2,4,-8,16,-32,….③
(1)第①行第8个数为______;第②行第8个数为______;第③行第8个数为______;
(2)第③行中是否存在连续的三个数,使得三个数的和为768?若存在,则求出这三数;不存在,则说明理由.
2,-4,8,-16,32,-64,…; ①
4,-2,10,-14,34,-62,…;②
1,-2,4,-8,16,-32,….③
(1)第①行第8个数为______;第②行第8个数为______;第③行第8个数为______;
(2)第③行中是否存在连续的三个数,使得三个数的和为768?若存在,则求出这三数;不存在,则说明理由.
![观察下面三行数:2,-4,8,-16,32,-64,…; ①4,-2,10,-14,34,-62,…;②1,-](/uploads/image/z/15341467-67-7.jpg?t=%E8%A7%82%E5%AF%9F%E4%B8%8B%E9%9D%A2%E4%B8%89%E8%A1%8C%E6%95%B0%EF%BC%9A2%EF%BC%8C-4%EF%BC%8C8%EF%BC%8C-16%EF%BC%8C32%EF%BC%8C-64%EF%BC%8C%E2%80%A6%EF%BC%9B%26nbsp%3B%E2%91%A04%EF%BC%8C-2%EF%BC%8C10%EF%BC%8C-14%EF%BC%8C34%EF%BC%8C-62%EF%BC%8C%E2%80%A6%EF%BC%9B%E2%91%A11%EF%BC%8C-)
(1)∵2,-4,8,-16,32,-64,…; ①
∴21=2,-4=-22,8=23,-16=-24,…
∴第①行第8个数为:-28=-256;
∵4,-2,10,-14,34,-62,…都比第一行对应数字大2,
∴第②行第8个数为:-254;
∵1,-2,4,-8,16,-32,….③
∴第③行是第一行的
1
2
∴第③行第8个数为:-128;
故答案为:-256,-254,-128;
(2)设第3个的数和为:(-1)n+1×2n-1+(-1)n+2×2n+(-1)n+3×2n+1=768,
当n为偶数:整理得出:-5×(-2)n-1=768,则求不出整数,
当n为奇数:整理得出:3×2n-1=768,解得:n=9.
∴这3个数为:256,-512,1024.
∴21=2,-4=-22,8=23,-16=-24,…
∴第①行第8个数为:-28=-256;
∵4,-2,10,-14,34,-62,…都比第一行对应数字大2,
∴第②行第8个数为:-254;
∵1,-2,4,-8,16,-32,….③
∴第③行是第一行的
1
2
∴第③行第8个数为:-128;
故答案为:-256,-254,-128;
(2)设第3个的数和为:(-1)n+1×2n-1+(-1)n+2×2n+(-1)n+3×2n+1=768,
当n为偶数:整理得出:-5×(-2)n-1=768,则求不出整数,
当n为奇数:整理得出:3×2n-1=768,解得:n=9.
∴这3个数为:256,-512,1024.
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