偏导数都存在只是全微分存在的充分条件而不是必要条件
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Which of the following laws explains how motors、generators and transformers work? ( )
A. Lenz’s law
B. Faraday’s law
C. Ampere’s law
For a Y connection, the line current IL is( )
A. Equal to phase current IL=Ip
B. Equal to square root 3 times phase current IL=1.73Ip
C. Equal to phase current divided by square root three IL=Ip/1.73
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