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maths m1

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(a)using the binomial theorem,expand (x+1)^77. (b)hence prove that when 81^77 is divided by 100,the remainder is 61. 點解AND 點做

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a. (x+1)^77 = Σ(r=0,77) 77Cr x^r b. Put x = 80, 81^77= Σ(r=0,77) 77Cr 80^r For r >= 2, it is divisible by 100, only when r = 0 and 1, it may not be divisible by 100, By checking this two term, Sum of the two term = 77C0 + 77C1 * 80 = 6161 6161/100 = 61 ... 61 Therefore, the remainder = 61

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