题目

设函数f(x)＝2x＋a·2－x－1(a为实数)．若a<0，用函数单调性定义证明：y＝f(x)在(－∞，＋∞)上是增函数． 答案：解析 设任意实数x1<x2， 则f(x1)－f(x2) ∴f(x1)－f(x2)<0，∴f(x)是增函数． A birthday is always a special celebration. It’s important to enjoy yourself because it’s the day out of the year that belongs to you. 【1】.Plan a get-together【2】. On your birthday, it’s important to spend time with those who will put a smile on your face. If you don’t have time to send out invitations, casually invite your guests over the phone at least a week in advance. Make sure they understand that it’s not a big formal dinner, but rather a casual get-together. 【3】. And you would love them to spend time with you on your birthday. If you aren’t in the mood to cook a big dinner, make reservations at your favorite restaurant.【4】Day trips are a wonderful birthday activity for those with a busy lifestyle. A week before the date, look into places around you that you’ve always wanted to visit. It may be a city, a rural countryside or a mountain resort. Regardless, it should be a place where you can relax and get away from your busy lifestyle. You can invite a few friends along, or just take the trip yourself.Spoil yourselfOn your birthday, it’s perfectly understandable to be a little selfish. Treating yourself on your birthday is the best gift you can give yourself after being financially responsible all year long. 【5】. Do little things that you never think to do for yourself when you’re busy running around. We all deserve a little pat on the back once in a while for our efforts, and birthdays are the perfect time to do it.A. Be yourself at homeB. Get away for the dayC. A quiet and relaxing place is your priorityD. Invite a few friends over for drinks and dinnerE. Let them know that you appreciate their companyF. There are plenty of ways to make the big day memorableG. Purchase the shirt you’ve been eyeing in the storefront window