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用第一换元法求定积分<img align="middle" alt="" src="/api/uploads/60000061943/in-rich-contentcreated_at=1648696608">，则下列步骤中正确的是（ ）．(单选题)
.<img align="middle" alt="" src="/api/uploads/60000061944/in-rich-contentcreated_at=1648696608">
.<img align="middle" alt="" src="/api/uploads/60000061945/in-rich-contentcreated_at=1648696608">
.<img align="middle" alt="" src="/api/uploads/60000061946/in-rich-contentcreated_at=1648696608">
.<img align="middle" alt="" src="/api/uploads/60000061947/in-rich-contentcreated_at=1648696608">

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出自：2024年国家开放大学答案

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