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问题 填空题

微分方程y"-3y’+2y=2ex满足

的特解为______．

答案

参考答案：y=-3ex+3e2x-2xex

解析：[详解] 特征方程为λ2-3λ+2=0，特征值为λ1=1，λ2=2，y"-3y’+2y=0的通解为y=C1ex+C2e2x．令原方程的特解为y0(x)=Axex，代入原方程为A=-2，原方程的通解为
y=C1ex+C2ex-2xex
由[*]．代入通解得C1=-3，C2=3，特解为y=-3ex+3e2x-2xex．

填空题
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单项选择题

New rules and behavior standards(行为规范) for middle school students came out in March. The Middle School is going to use a new way to decide who the top students are. The best students won’t only have high marks. They should not (染) their hair, smoke or drink because they are students. The following are some of the new rules.
Have you ever copied someone else’s work in an exam Don’t do that again! That’s not something an honest student should do.
Do more at school. Good students love animals and care for other people. April is Bird-loving Month in China. Is your school doing anything to celebrate it You should join! And you can learn more about animals and how to protect them. Be friendly to the people around you. Try to think of others, not only yourself.
Be open to new ideas. Do you think people can live on the moon7 Maybe you’ll find another earth someday. Don’t look down on new ideas. Everyone’s ideas are important. You should welcome them, because new ideas make life better for everyone.
Protect yourself. Has someone ever taken money from one of your classmates Don’t let it happen to you. If you have to go home late, you should let your parents know.
Use the Internet carefully. The Internet can be very useful for students. But some things on the Internet aren’t for children, so try to look at web pages (网页) that are good for you.

What’s the meaning of "look down on" in the passage

A．向下看

B．轻视

C．在……上面看

D．上下打量
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