题目

We all think that we know what happiness is. We all seem to be making great efforts towards this goal of happiness but what is it really? It is an agreed fact that all the creatures want happiness and are afraid of pain and sadness. The question, however, is “what is real happiness?” What really is called happiness? The desire for happiness has no meaning without understanding the real nature of happiness. Some thinkers say, “Happiness does not lie in objects of enjoyment; happiness or unhappiness lies in imagination.” To prove their belief, they give examples like the following 已知(ax＋1)7(a≠0)的展开式中，x3的系数是x2的系数与x4的系数的等差中项，求a；