What does the "difference of squares formula" mentioned by fujoshi mean?

It is the formula of square X, - - the difference is pronounced as cha.. Do you understand?

╮(╯▽╰)╭ Let me give you a joke...

One day the dormitory was talking about the adulterer Yinfu in Chinese history.

A then spoke eloquently: Isn’t this simple? There are seven major adulterers in Chinese history, the hoeing day is at noon, hematopoietic stem cells, the Riverside Scene during the Qingming Festival, the compound grass coral, the square difference formula, the squad leader and the school committee, I can't understand it at all.

Everyone except B laughed wildly.

C asked B: Does it feel boring?

B replied calmly: You are all out of date. There is also a saying that there are nine adulterers and silver men in Chinese history. They bent their bows to shoot big eagles, Legend of Fairy Sword and Fairy Heroes, Dynasty Dry Red Wine, Double Ninth Festival planted dogwood, the Yellow River flows into the sea, they dance to clear their shadows, and egrets ascend to the blue sky. Pear blossoms press against begonias, winding paths lead to secluded places