The second chapter is the sequence, mainly studying arithmetic progression and geometric progression, focusing on four formulas, and the summation problem is more difficult;

Chapter III Inequality. First, we learn the essence of inequality, which is not much different from that of junior middle school. Then it is not difficult to learn the solution of a quadratic inequality (mainly relying on quadratic function images). There is also a mean inequality (mainly the transformation of conditions), which is a bit difficult but not big.