题干

圆x2+y2﹣4x﹣4y﹣10=0上的点到直线x+y﹣8=0的最大距离与最小距离的差是(   )

A:18

B:6 2

C:5 2

D:4 2

上一题 下一题 0.0难度 选择题 更新时间:2018-06-14 10:38:34

答案(点此获取答案解析)

B

同类题1

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    You're not doomed to toss and turn every night. Although you might not be able to control all of the factors that relate to your sleep, you can adopt habits that encourage better sleep. Start with these simple sleep tips.

    No. 1: Stick to a sleep schedule

    Go to bed and get up at the same time every day, even on weekends, holidays and days off. Being consistent reinforces (加强) your body's sleep-wake cycle and helps promote better sleep at night. If you don't fall asleep within about 15 minutes, get up and do something relaxing. Go back to bed when you're tired.

    No. 2: Pay attention to what you eat and drink

    Don't go to bed either hungry or stuffed. Your discomfort might keep you up. Also limit how much you drink before bed, to prevent disruptive middle-of-the-night trips to the toilet. Nicotine, caffeine and alcohol deserve caution, too. The stimulating effects of nicotine and caffeine — which take hours to wear off — can ruin quality sleep.

    No. 3: Create a bedtime ritual

    Do the same things each night to tell your body it's time to wind down. This might include taking a warm bath or shower, reading a book, or listening to light music. Be careful of using the TV or other electronic devices as part of your bedtime ritual. Some research suggests that screen time or other media use before bedtime has impact on sleep.

    No. 4: Get comfortable

    Create a room that's ideal for sleeping. Often, this means cool, dark and quiet. Consider using room-darkening shades, earplugs, a fan or other devices to create an environment that suits your needs.

    Your mattress and pillow can contribute to better sleep, too. Since the features of good bedding are subjective, choose what feels most comfortable to you. If you have children or pets, set limits on how often they sleep with you — or insist on separate sleeping quarters.

    No. 5: Limit daytime naps

    Long daytime naps can affect nighttime sleep — especially if you're struggling with poor sleep quality at night. If you choose to nap during the day, limit yourself to about 10 to 30 minutes and make it during the mid-afternoon.

If you work nights, you'll need to make an exception to the rules about daytime sleeping. In this case, keep your window coverings closed so that sunlight — which adjusts your internal clock — doesn't interrupt your daytime sleep.

    No. 6: Include physical activity in your daily routine

    Regular physical activity can promote better sleep, helping you to fall asleep faster and to enjoy deeper sleep. Timing is important, though. If you exercise too close to bedtime, you might be too energized to fall asleep. If this seems to be an issue for you, exercise earlier in the day.

    No. 7: Manage stress

    When you have too much to do — and too much to think about — your sleep is likely to suffer. To help restore peace to your life, consider healthy ways to manage stress. Start with the basics, such as getting organized, setting priorities and dividing tasks. Give yourself permission to take a break when you need one. Share a good laugh with an old friend.

    Nearly everyone has an occasional sleepless night — but if you often have trouble sleeping, contact your doctor. Identifying and treating any underlying causes can help you get the better sleep you deserve.

同类题2

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