The first method is a big problem. Sort out that (root number a-2)+ (root number A-3) is less than or equal to (root number A-2)+(root number A- 1). Both sides of the formula are greater than 0, and the square formula holds the second method √ a-√ (a-1) = [√ a-√ (a-1)]/[√ a √ (a-65438)