87÷4=（ ） A: 21…3 B: 20…7 C: 22…1
87÷4=（ ） A: 21…3 B: 20…7 C: 22…1
（接上题）（2）设经分界面反射的波的振幅和入射波的振幅相等，则反射波的波函数是 A: $y_{r}=Acos \left(2\pi \nu t+\dfrac{2\pi\nu}{u}x-\dfrac{\pi}{2} \right),0\le x\le\dfrac{3\lambda}{4}$ B: $y_{r}=Acos \left(2\pi \nu t+\dfrac{2\pi\nu}{u}x \right),0\le x\le\dfrac{3\lambda}{4}$ C: $y_{r}=Acos \left(2\pi \nu t+\dfrac{2\pi\nu}{u}x-\dfrac{\pi}{4} \right),0\le x\le\dfrac{3\lambda}{4}$ D: $y_{r}=Acos\left(2\pi \nu t-\dfrac{2\pi\nu}{u}x \right),0\le x\le\dfrac{3\lambda}{4}$
（接上题）（2）设经分界面反射的波的振幅和入射波的振幅相等，则反射波的波函数是 A: $y_{r}=Acos \left(2\pi \nu t+\dfrac{2\pi\nu}{u}x-\dfrac{\pi}{2} \right),0\le x\le\dfrac{3\lambda}{4}$ B: $y_{r}=Acos \left(2\pi \nu t+\dfrac{2\pi\nu}{u}x \right),0\le x\le\dfrac{3\lambda}{4}$ C: $y_{r}=Acos \left(2\pi \nu t+\dfrac{2\pi\nu}{u}x-\dfrac{\pi}{4} \right),0\le x\le\dfrac{3\lambda}{4}$ D: $y_{r}=Acos\left(2\pi \nu t-\dfrac{2\pi\nu}{u}x \right),0\le x\le\dfrac{3\lambda}{4}$
（2）设经分界面反射的波的振幅和入射波的振幅相等，则反射波的波函数是 A: $y_{r}=Acos \left(2\pi \nu t+\dfrac{2\pi\nu}{u}x-\dfrac{\pi}{2} \right),0\le x\le\dfrac{3\lambda}{4}$ B: $y_{r}=Acos \left(2\pi \nu t+\dfrac{2\pi\nu}{u}x \right),0\le x\le\dfrac{3\lambda}{4}$ C: $y_{r}=Acos \left(2\pi \nu t+\dfrac{2\pi\nu}{u}x-\dfrac{\pi}{4} \right),0\le x\le\dfrac{3\lambda}{4}$ D: $y_{r}=Acos\left(2\pi \nu t-\dfrac{2\pi\nu}{u}x \right),0\le x\le\dfrac{3\lambda}{4}$
（2）设经分界面反射的波的振幅和入射波的振幅相等，则反射波的波函数是 A: $y_{r}=Acos \left(2\pi \nu t+\dfrac{2\pi\nu}{u}x-\dfrac{\pi}{2} \right),0\le x\le\dfrac{3\lambda}{4}$ B: $y_{r}=Acos \left(2\pi \nu t+\dfrac{2\pi\nu}{u}x \right),0\le x\le\dfrac{3\lambda}{4}$ C: $y_{r}=Acos \left(2\pi \nu t+\dfrac{2\pi\nu}{u}x-\dfrac{\pi}{4} \right),0\le x\le\dfrac{3\lambda}{4}$ D: $y_{r}=Acos\left(2\pi \nu t-\dfrac{2\pi\nu}{u}x \right),0\le x\le\dfrac{3\lambda}{4}$
设(X,Y)的分布律为[img=317x47]1803c4763fc5f8e.png[/img]U=XY, 则P(U=1)等于 A: 4/7 B: 3/7 C: 2/7 D: 1/7
设(X,Y)的分布律为[img=317x47]1803c4763fc5f8e.png[/img]U=XY, 则P(U=1)等于 A: 4/7 B: 3/7 C: 2/7 D: 1/7
设(X,Y)的分布律为[img=317x47]17de6694cf27b19.png[/img]U=XY, 则P(U=1)等于 A: 4/7 B: 3/7 C: 2/7 D: 1/7
设(X,Y)的分布律为[img=317x47]17de6694cf27b19.png[/img]U=XY, 则P(U=1)等于 A: 4/7 B: 3/7 C: 2/7 D: 1/7
设(X,Y)的分布律为[img=317x47]180306cf74acc90.png[/img]U=XY, 则P(U=1)等于 A: 4/7 B: 3/7 C: 2/7 D: 1/7
设(X,Y)的分布律为[img=317x47]180306cf74acc90.png[/img]U=XY, 则P(U=1)等于 A: 4/7 B: 3/7 C: 2/7 D: 1/7
设(X,Y)的分布律为[img=317x47]1803a655b691efe.png[/img]U=XY, 则P(U=1)等于 A: 4/7 B: 3/7 C: 2/7 D: 1/7
设(X,Y)的分布律为[img=317x47]1803a655b691efe.png[/img]U=XY, 则P(U=1)等于 A: 4/7 B: 3/7 C: 2/7 D: 1/7
设(X,Y)的分布律为[img=317x47]1803a2cb5c8d407.png[/img]U=XY, 则P(U=1)等于 A: 4/7 B: 3/7 C: 2/7 D: 1/7
设(X,Y)的分布律为[img=317x47]1803a2cb5c8d407.png[/img]U=XY, 则P(U=1)等于 A: 4/7 B: 3/7 C: 2/7 D: 1/7
设(X,Y)的分布律为[img=317x47]1803a0ae2ea89a8.png[/img]U=XY, 则P(U=1)等于 A: 4/7 B: 3/7 C: 2/7 D: 1/7
设(X,Y)的分布律为[img=317x47]1803a0ae2ea89a8.png[/img]U=XY, 则P(U=1)等于 A: 4/7 B: 3/7 C: 2/7 D: 1/7
设(X,Y)的分布律为[img=242x36]17e43948588a464.png[/img]U=XY, 则P(U=1)等于 A: 4/7 B: 3/7 C: 2/7 D: 1/7
设(X,Y)的分布律为[img=242x36]17e43948588a464.png[/img]U=XY, 则P(U=1)等于 A: 4/7 B: 3/7 C: 2/7 D: 1/7