【简答题】若方程组 x 2 + y 2 =34 x-y=6 的解为 x= x 1 y= y 1 , x= x 2 y= y 2 求:(1) x 21 + x 22 (2) 1 y 1 + 1 y 2 .
【单选题】已知点(x 1 ,y 1 ),(x 2 ,y 2 )均在抛物线y=x 2 -1上,下列说法中正确的是( )
B.
若x 1 =-x 2 ,则y 1 =-y 2
C.
若0<x 1 <x 2 ,则y 1 >y 2
D.
若x 1 <x 2 <0,则y 1 >y 2
【单选题】下列结论正确的是( )
A.
若y=x+ 1 x ,则y′=1+ 1 x 2
C.
若y= x e x ,则y′= 1-x e x
【简答题】若X 1 ~X 2 ,Y 1 ~Y 2 ,且X 1 ∩Y 1 =X 2 ∩Y 2 = ,证明: X 1 ∪Y 1 ~X 2 ∪Y 2 .
【简答题】选词填空。 down lost go stop 1. When the traffic light is red, we must _____________. 2. When the traffic light is green, we can _____________. 3. I'm _____________. Where's the hotel? 4. Go...
【简答题】Look and answer. (看图,回答问题) 1 . How do you feel? ____________________________________ 2. How do they feel? ____________________________________ 3. What's the matter with him? __________________________...