题目

There are three kinds of goals: short-term, medium-term and long-term goals. Short-term goals are those that usually deal with current activities, which we can apply on a daily basis. Such goals can be achieved in a week or less, or two weeks, or possible months. It should be remembered that just as a building is no stronger than its foundation, our long-term goals cannot mean very much without the achievement of solid short-term goals. Upon completing our short-term goals, we should date the occasion and then add new short-term goals that will build on those that have been completed.今年“五一”期间，小明准备攀登海拔高度为2000米的山峰．导游介绍山区气温会随着海拔高度的增加而下降，提醒大家上山要多带一件衣服，小明从网上查到该山区海拔和即时气温的部分数据表，数据如下：海拔高度x（米）400500600700800…气温y（℃）29.228.628.027.426.8…（1）以海拔高度为x轴，根据上表提供的数据在下列直角坐标系中描点并连线；（2）观察（1）中所画出的图象，猜想与之间函数关系，求出所猜想的函数关系表达式，并根据表中提供的数据验证你的猜想；（3）如果气温低于20℃就需要穿外套，请问小明需不需要携带外套上山？