[(1/31+1/37+1/41+1/47+1/53+1/69)*(1/29+1/31+1/37+1/41+1/47+1/53
题目
[(1/31+1/37+1/41+1/47+1/53+1/69)*(1/29+1/31+1/37+1/41+1/47+1/53
)]-[(1/29+1/31+1/37+1/41+1/47+1/53+1/69)*(1/31+1/37+1/41+1/47+1/53)]
答案
设 a=1/31+1/37+1/41+1/47+1/53,b=1/29+1/31+1/37+1/41+1/47+1/53
原式=(a+1/69)b-(b+1/69)a=ab-ba+1/69 * (b-a)=1/(69*29)=1/(69*29)
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