做成了第一架望远镜

feels empty

essay啥时候能写完啊

different from before
differentiate both sides等式2边同时求导

integral both sides同求积分

越来越渺茫的看不见你想要或是应有的维持

determinant and subdeterninant is a 确定的值

一个晚上搞完了2个作业和一篇回帖 治杀

infinitely many solutions 无穷多个解

arbitrary constant任意的常数

充分条件(Sufficient condition );
必要条件( prerequisite);
充分必要条件(sufficient prerequisite);
必要充分条件(necessary sufficient condition).

distinct solution 不同的解

bisects the area 平分面积