某三相电路中A，B，C三相的有功功率分别为PA，PB，PC，则该三相电路总有功功率P为（ ）。
A:
B:
C:
A:
B:
C:
举一反三
- 在常体力的情况下，平面问题的应力函数与应力分量之间的关系正确的有（ ）。 A: <img src="https://image.zhihuishu.com/zhs/doctrans/docx2html/202102/13db38e0be0f42a8aa8220026ad6d3e5.png">，<img src="https://image.zhihuishu.com/zhs/doctrans/docx2html/202102/9178e461e0974317b42e0e9b59149047.png">，<img src="https://image.zhihuishu.com/zhs/doctrans/docx2html/202102/d66f684595a1482283e180c311c9e8f4.png"> B: <img src="https://image.zhihuishu.com/zhs/doctrans/docx2html/202102/20a366b5fd844f65a1716a7a6078b968.png">，<img src="https://image.zhihuishu.com/zhs/doctrans/docx2html/202102/f4a5a69f1a264e5b8f28fa968022cbb0.png">，<img src="https://image.zhihuishu.com/zhs/doctrans/docx2html/202102/b77e7d17deb548619be88f5ed437af81.png"> C: <img src="https://image.zhihuishu.com/zhs/doctrans/docx2html/202102/cb0ce22cc89447b5b3a914b1a55209a0.png">，<img src="https://image.zhihuishu.com/zhs/doctrans/docx2html/202102/d56afcca319e46a2be256f91ac5e289b.png">，<img src="https://image.zhihuishu.com/zhs/doctrans/docx2html/202102/d6a4d2e83f9448cdbfec37887ffd53a9.png"> D: <img src="https://image.zhihuishu.com/zhs/doctrans/docx2html/202102/1f5fa1a13a4c48698715e2b1814291b4.png">，<img src="https://image.zhihuishu.com/zhs/doctrans/docx2html/202102/06c0cb7f6e184b18a6b345acff91e4bb.png">，<img src="https://image.zhihuishu.com/zhs/doctrans/docx2html/202102/c59f70ea241546dd948d2f09b5821ac6.png">
- 双纽线<img src="https://image.zhihuishu.com/zhs/doctrans/docx2html/202102/ac4dfd0de9744513843c41341938f31c.png" />所围成的区域面积可用定积分表示为（ ） A: <img src="https://image.zhihuishu.com/zhs/doctrans/docx2html/202102/b3a266adc8704187b18601cd19efc069.png" /> <img src="https://image.zhihuishu.com/zhs/doctrans/docx2html/202102/fbc5959fd78d4d09ae216f05e45741c0.png" />. <img src="https://image.zhihuishu.com/zhs/doctrans/docx2html/202102/02b5a6e0e400485382b137795ebb9ef1.png" /> B: <img src="https://image.zhihuishu.com/zhs/doctrans/docx2html/202102/45fb209600124a569d31e4c0ed4264f9.png" /> C: <img src="https://image.zhihuishu.com/zhs/doctrans/docx2html/202102/d5291bc308bc4880919d6f34ce4f7539.png" />
- 下面和声连接对的是（ ） A: <img src="https://image.zhihuishu.com/zhs/doctrans/docx2html/202102/cfbbaacbd31140caada6de1a82879cf1.jpeg" /> B: <img src="https://image.zhihuishu.com/zhs/doctrans/docx2html/202102/cfbbaacbd31140caada6de1a82879cf1.jpeg" /> C: <img src="https://image.zhihuishu.com/zhs/doctrans/docx2html/202102/cfbbaacbd31140caada6de1a82879cf1.jpeg" /> D: <img src="https://image.zhihuishu.com/zhs/doctrans/docx2html/202102/cfbbaacbd31140caada6de1a82879cf1.jpeg" />
- 坐标系{B}相对于坐标系{A}绕Z轴旋转<img src="https://image.zhihuishu.com/zhs/doctrans/docx2html/202102/0e7f1303cace4a9fa888211d1b94e3c3.png" />度，坐标系{B}中的矢量<img src="https://image.zhihuishu.com/zhs/doctrans/docx2html/202102/06f5b17a51fb43deb2e94fe685b5b511.png" />在{A}中的坐标表示为（ ）。 A: <img src="https://image.zhihuishu.com/zhs/doctrans/docx2html/202102/86783ba498314fdfa0c22abffc2891f2.png" /> B: <img src="https://image.zhihuishu.com/zhs/doctrans/docx2html/202102/ea644ea443b74b54b41c89eff9db781a.png" /> C: <img src="https://image.zhihuishu.com/zhs/doctrans/docx2html/202102/dddcfd36e178435c8a82f63cc982fd2b.png" /> D: <img src="https://image.zhihuishu.com/zhs/doctrans/docx2html/202102/1d5f3187c48f447eb117b0005e7ca646.png" />
- 若某系统的传递函数为G(s)=<img src="https://image.zhihuishu.com/zhs/doctrans/docx2html/202102/79eaf52d33de48cd9c870f2ce2ace2dc.png" />，则其频率特性的实部R(ω)是（ ） A: <img src="https://image.zhihuishu.com/zhs/doctrans/docx2html/202102/22de2385b19e4de8be5ae000bddad620.png" /> B: <img src="https://image.zhihuishu.com/zhs/doctrans/docx2html/202102/4a873e7d91b44c11bad767efd2747b11.png" /> C: -<img src="https://image.zhihuishu.com/zhs/doctrans/docx2html/202102/4a873e7d91b44c11bad767efd2747b11.png" /> D: -<img src="https://image.zhihuishu.com/zhs/doctrans/docx2html/202102/22de2385b19e4de8be5ae000bddad620.png" />