在△ABC中，a、b、c分别是角A、B、C所对的边，满足a2+c2-b2=ac．
（1）求角B的大小；
（2）若x∈[0，π），求函数f（x）=sin（x-B）+sinx的值域．
（1）在△ABC中，由余弦定理得cosB=
=a2+c2-b2 2ac 1 2
又∵B∈(0，π)，∴B=
；π 3
（2）f(x)=sin(x-
)+sinx=π 3
sinx-3 2
cosx=3 2
sin(x-3
)π 6
∵0≤x＜π，则-
≤x-π 6
＜π 6 5π 6
∴sin(x-
)∈[-π 6
，1]1 2
Do you blank out, freeze up or feel so nervous in exams that you have trouble writing answers to questions that you knew just last night? If so, you likely have a case of test anxiety. But, don’t panic. By recognizing the problem, you are taking the first step towards overcoming it. Believe it or not, a touch of nervousness can sharpen your mind, allowing you to perform more quickly. This is because under stress, the body releases the hormone adrenaline (肾上腺素), which prepares it for something important that will happen. However, too much anxiety can result in sleeplessness, loss of appetite（食欲） before tests, and poor performances. Some people might feel shaky, hot, or even sick. If you worry a lot or are a perfectionist, you are more likely to have trouble with test anxiety. Those who have prepared poorly for a test or have had negative experiences taking tests may also experience test anxiety. When you feel a storm of anxiety coming on, stop what you are doing and make your mind a blank. If possible, actually tell yourself to “STOP”. This will get your mind off the stress. Then think of being at a place of comfort and let your body relax. As you continue the test, find questions you know the answers to and answer them first. This will help restore your confidence. Talk to yourself using positive language. Make it a habit to replace each negative thought with a logical reason. For example：“ I’ve studied hard and I know the material, so I’m ready to do the best I can.” Another thing you can do is to learn to accept mistakes. In fact, they can be valuable learning opportunities. Last but not least, start test preparation early---three to five days ahead of the quiz or test. After all, good study habits and skills ---for example, time management and note-taking – will give you the feeling that your are in control. 小题1:The first step to overcome nervousness is___ .
|
ou are always nervous
.