① <img class=jc-formula style=vertical-align: middle; src=https://huaweicloudobs.ahjxjy.cn/D5A6F8981882EB832EF1EF2D47534C8D.png data-tex=cos\varphi =0.5,R=15\Omega ,{ X }_{ L }=16.1\Omega />
② <img class=jc-formula style=vertical-align: middle; src=https://huaweicloudobs.ahjxjy.cn/5C4C3196D1110576D4461A65FB0E9490.png data-tex=cos\varphi =0.682,R=15\Omega ,{ X }_{ L }=16.1\Omega />
③ <img class=jc-formula style=vertical-align: middle; src=https://huaweicloudobs.ahjxjy.cn/5723BC0EA51626B821293278E60D4474.png data-tex=cos\varphi =0.682,R=16.1\Omega ,{ X }_{ L }=15\Omega />
④ <img class=jc-formula style=vertical-align: middle; src=https://huaweicloudobs.ahjxjy.cn/24C4607E78F40A9829ADB1518F6E1FE4.png data-tex=cos\varphi =0.6,R=15\Omega ,{ X }_{ L }=16.1\Omega />
【单选题】
2-1 求题图2-1所示电路的输入电阻<img class=jc-formula data-tex={ R }_{ ab } src=https://huaweicloudobs.ahjxjy.cn/6C6E461520C684943C6A930FE5BDF18E.png style=vertical-align: middle;/>。<img src=https://huaweicloudobs.ahjxjy.cn/5B3EF66A642BC4FD8C9FBBC1FF7D1E09.png title=2-1.PNG alt=2-1.PNG/>
① <img class=jc-formula data-tex={ R }_{ ab }=3\Omega src=https://huaweicloudobs.ahjxjy.cn/7F8664EFB8C75064D1D4ABEB5392C174.png style=vertical-align: middle;/>
② <img class=jc-formula data-tex={ R }_{ ab }=4\Omega src=https://huaweicloudobs.ahjxjy.cn/B30A8F74BCB7C356DAEC7404DCC96E2F.png style=vertical-align: middle;/>
③ <img class=jc-formula data-tex={ R }_{ ab }=3.4\Omega src=https://huaweicloudobs.ahjxjy.cn/A318A3B99CF30192A7E63F595A58F653.png style=vertical-align: middle;/>
④ <img class=jc-formula data-tex={ R }_{ ab }=4.4\Omega src=https://huaweicloudobs.ahjxjy.cn/A7F0D3B2C8B0E001E5889D9054C3FA97.png style=vertical-align: middle;/>