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If `9^7-7^9`is divisible b `2^n ,`then find the greatest value of `n ,w h e r en in Ndot` |
Answer» We have `9^(7)-7^(9) = (1+8)^(7) - (1-8)^(9)` `= (1+.^(7)C_(1)8^(1)+.^(7)C_(2)8^(2)+"….."+.^(7)C_(7)8^(7)) - (1-.^(9)C_(1)8^(1)+.^(9)C_(2)8^(2)-"……."-.^(9)C_(9)8^(9))` `= 16xx8+64[(.^(7)C_(2)+"….."+.^(7)C_(7)8^(5))-(.^(9)C_(2)-"……"-.^(9)C_(9)8^(7))]` `= 64k` (where k is some integer ) Therefore, `9^(7) - 7^(9)` is divisible by `64`. |
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