[微積] 高微一題

[HipHopBoy (嘻哈男孩)]

                                   β
f is Riemann integrable on [a,b]，∫ f(x)dx = 0，for all a<=α<=β<=b
                                   α
            b
prove that ∫|f(x)|dx = 0
            a

不知如何下手 懇請解答 感謝

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◆ From: 114.43.114.30
→ wickeday    :{x:f(x)>0} is open in [a,b]
推 zombiea     :f may not be conti
→ zombiea     :write f=f_+ - f_-, reduce to f is positive
→ zombiea     :then get contradiction via go through the defini.