【简答题】If y 2 =2x where x and y are real numbers, then the minimum value of z=y 2 +x 2 +4 is ( ). (A)3. (B)4. (C)5. (D)6.
【单选题】Which set is a proper subset of E? ( ) E= {0,1,2,3}
A.
{ x|x is a real number and x—3=0}
B.
{ x|x is a real number and x2—9}
C.
{ x|x is a real number and x2+5x+6=0}
【判断题】If x is a real number, then |-x| = x .
【单选题】syms x real; A=simplify(sin(x)^2+cos(x)^2); 则A= ( ) 。
【单选题】下列说法中哪一种是错误的?( )
C.
边际产量曲线一定在平均产量曲线的最高点与之相交
【简答题】Advertising______in 2009 ensured that the song by The X Factor winner did not become number one by Christmas.
【单选题】下列说法中哪种是错误的?
D.
反应的活化能越大,升高温度时反应速率增加得就越快