题目

When Dave was eighteen, he bought a secondhand car for 200 dollars so that he could travel to and from work more__41__ than by bus. It worked quite well for a few years, but then it got so old, and it was costing him _42_much in repairs that he decided that he had better _43_it.He asked among his friends to see if anyone was particularly_ 44_ to buy a cheap car, but they all knew that it was falling to pieces, so_45_ of them had any desire（愿望） to buy it. Dave's friend Sam saw that he was _46_ when they met one evening, and said, “What's _47_, Dave?”Dave told him, and Sam an1．先化简，再求值：1-$\frac{x-y}{x+2y}$÷$\frac{{x}^{2}-{y}^{2}}{{x}^{2}+4xy+4{y}^{2}}$，其中x=-2，y=1．