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The sequence of numbers $$a_1,a_2,a_3,...,a_n...$$is defined by$$a_n=\frac{1}{n}-\frac{1}{n+2}$$for each integer n≥1.What is the sum of the first 20 terms of this sequence?
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A.$$(1+\frac{1}{2})-\frac{1}{20}$$
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B.$$(1+\frac{1}{2})-(\frac{1}{21}+\frac{1}{22})$$
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C.$$1-(\frac{1}{20}+\frac{1}{22})$$
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D.$$1-\frac{1}{22}$$
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E.$$\frac{1}{20}-\frac{1}{22}$$
B显示答案
