听下面5个小题中的字母和单词,然后从题中所给的ABC三个选项中选择最佳答案,并标在答卷的相应 位置,听完每个小题你都有5秒钟的时间来回答有题和阅读下一小题。每个小题读两遍。 ( )1. A. Aa ( )2. A. apple ( )3. A. class ( )4. A. open ( )5. A. lesson B. Hh B. China B. practice B. ride B. can C. LI C. coat C. doctor C. sixteen C. people
【单选题】A motor drives a shaft at f=10 Hz and delivers P= 35 kW of power. The allowable shear stress in the shaft is 45 MPa. The minimum diameter of the shaft is approximately:【图片】
【多选题】If a point x* is a minimum of the function f(x) under the constrained condition g(x)=0, the first-order necessary for the condition extremum includes ( )
A.
f(x*)=0
B.
g(x*)=0
C.
▽f(x*)=0 [the gradient of the function f at the point x* is equal to zero vector]