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用第一换元法求不定积分<img align="middle" alt="" src="/api/uploads/1529834/in-rich-contentcreated_at=1647290117">，则下列步骤中正确的是（　）．(单选题)
.<img align="\"middle\"" alt="\"\"" src="\"/api/uploads/1529836/in-rich-contentcreated_at=1647290117\"">.,.
<img align="\"middle\"" alt="\"\"" src="\"/api/uploads/1529837/in-rich-contentcreated_at=1647290117\"">.,.
<img align="\"middle\"" alt="\"\"" src="\"/api/uploads/1529838/in-rich-contentcreated_at=1647290117\"">.,.
<img align="\"middle\"" alt="\"\"" src="\"/api/uploads/1529835/in-rich-contentcreated_at=1647290117\"">

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出自：2024年国家开放大学答案

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