=∫[0→π] 1 dx - ∫[0→π] cos？ x dx
=π - ∫[0→π] cos？ x dsinx
=π - ∫[0→π] ( 1-sin？ x) dsinx
=π - [sinx - ( 1/3)sin？ x] |[0→π]
=π
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