设S(x)=∫0x|cosx|dt· 证明:当nπ≤x<(n+1)π时,2n≤S(x)<2(n+1);

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问题 设S(x)=∫0x|cosx|dt·
证明:当nπ≤x<(n+1)π时,2n≤S(x)<2(n+1);

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答案当nπ≤x<(n+1)π时,∫0|cost|dt≤∫0π|cost|dt<∫0(n+1)π|cost|dt, ∫0|cost|dt=n∫0π|cost|dt=[*]=2n, ∫0(n+1)π|cost|dt=2(n+1),则2n≤S(x)<2(n+1).

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