In the evening, Qi Binxuan saw a little boy lying on the steps in front of the door doing his homework. I saw this little boy carrying a large schoolbag, squatting on the ground, holding a ballpoint pen in his hand and writing carefully stroke by stroke.

Qi Binxuan couldn't help but think that it was really not easy for children. Thinking that he seemed to have come from this step, he said to the child: "Child, are you tired of writing homework on your stomach?

The little boy glanced at Qi Binxuan and said, "The teacher said that you can't talk to strangers. ”

Qi Bin smiled and decided to tease him: "I'm the owner of this shop, you see, I've introduced myself, you can introduce yourself again." We're not strangers. ”

The little boy said, "Then I have to ask my mother." Then he took out the phone and dialed a number: "Hey, Mom, there is a shopkeeper who wants me to go to his store to do my homework, do you think it's okay? Ah, let him answer the phone? Boss, answer the phone." ”

Qi Bin answered the phone speechlessly: "Hey, ah, yes, I'm the owner of the Maker Tea House, and it's very hard to watch children do their homework outside, so let me come to the store to write." ...... Ah, you're Aunt Wang upstairs. That's my father. Yes, I just took over. Okay, you can come back and pick up the kids from my store. ”

Then Qi Binxuan returned the phone to the little boy, and the little boy said a few more words, and then went back to the store with Qi Binxuan to do his homework.

After entering the house, Qi Binxuan praised the little boy: "Yes, the vigilance is quite high." By the way, what's your name and what grade are you in?"

"My name is Feng Hao, and I'm in the seventh grade now. ”

"Okay, you can call me Brother Qi. You can do your homework by the window over there, and the light will be better. I'll make you a pot of tea. ”

Qi Binxuan was busy with other things at the counter. When he was done, he saw Feng Hao staring at the homework book there, frowning and biting the pen.

Qi Binxuan stepped forward and asked, "What's the matter, I can't meet a problem, let me see?"

"Will you? My mom said you little bosses don't study very well. Feng Hao said.

Qi Bin was unhappy and said, "Hey, why did your mother teach you like this?"

"Mom said that because your little boss is rich, you don't need to study. Feng Hao explained.

"Hiss-" Qi Binxuan gasped, hearing this explanation, he felt angry, unhappy, and indescribably awkward. Qi Binxuan couldn't help but admire: "Your mother has great wisdom." But you can't generalize. There are always exceptions. There must be my teacher in the threesome, do you know what it means?"

"You know, it's just three people walking, and one of them is a teacher. Feng Hao said disdainfully.

"Hey, are all the children nowadays so unique? Threesomes must have my teacher...... Forget it, don't explain, I'll see if you don't know the question. ”

"Won't you? It's a tough question, and my mom won't either. Feng Hao asked.

"Hey, anyway, we're college graduates. Can you not even know a seventh-grade question?" Qi Binxuan continued to joke with the little boy. Then I looked at the question: Oral Arithmetic, 2009×2007-2008².

Qi Binxuan smiled and said to the little boy: "That's it? Isn't this a negative one." It's so simple, you can't figure it out for half a day. ”

The little boy didn't believe it, and then Qi Binxuan explained to him that this is the application of square difference. 2009 and 2007 are decomposed into 2008 plus or minus 1 respectively, and then the square difference formula becomes 2008²-1²-2008², so that it looks like a minus one.

The little boy said that he understood it when he heard him, but he couldn't remember it when he was doing it.

Qi Bin teased him: "Is this one, that's because you didn't find an easy way." I have a cheat specifically for this square difference, guaranteed to be learned as soon as I learn it. ”

The little boy listened and said, "Really, then teach me quickly." ”

"That's not good, since it's a cheat, I can't give it to you for nothing. Say, what price are you going to pay to learn this cheat?"

"Why don't I buy you some sorbet?"

"No, I'm getting older, I don't have a good appetite, and I can't eat cold things. ”

"Then I'll give you today's pocket money, is ten dollars enough?"

Qi Bin said in his heart, children now have a lot of pocket money. Ten yuan a day, I thought that we could have five cents a day and be happy. But he still refused: "You see that I am the owner of a tea shop, can I look at your ten yuan?"

The little boy pondered quietly, rolling his eyes from time to time with a tangled expression. And Qi Binxuan picked up a cup of tea on the table and tasted it slowly. Just when Qi Binxuan was about to tell the little boy the "cheats" and stop teasing him, the little boy spoke.

I saw the little boy lower his voice and said weakly: "Why don't I introduce my sister to you?" She just graduated from college this year, got a job, and doesn't have a boyfriend yet. She hasn't gotten off work yet, so she'll introduce you to each other when she gets off work, and then we'll have dinner together. However, I am only responsible for introducing you to you, and it depends on your ability to succeed. ”

Qi Bin took a sip of tea and squirted out. No, we must correct the little boy's ideological concept, as a child, how can he do such a thing if he wants to be innocent and cute? So Qi Bin taught him a stern lesson: "Isn't it pretty, isn't it beautiful, don't I invite you to dinner?"

"Absolutely beautiful. The little boy reassured, as if he felt that the empty words were not convincing, and then looked around, pointed to Luo Hongyi, who was rubbing the table, and said, "It must be more beautiful than that sister." ”

Luo Hongyi looked up at the two of them and scolded with a smile: "Why did you two involve me too." I was shot while lying down. ”

Qi Bin said hello with a smile, and then said to the little boy: "Deal." I'm going to tell you the recipe for this squared difference formula. This cheat is a story. ”

"Story?" the little boy wondered, "Can't you lie to me if I was a child?"

"How could I lie to you. Do you know why most people prefer language to math?"

"Why?"

"Because there are a lot of stories and novels in the language, which is very interesting. Mathematics, on the other hand, is made up of a bunch of numbers and formulas, so many people are not interested. But that's just because they didn't find the right way, in fact, math has a story. I'm going to tell you the story of this squared difference formula. The name of this story is 'Fake Sword, Square Sword'. ”

Next, Qi Binxuan told Feng Hao the story of this square difference formula.

Once upon a time there was a family, just like ordinary people, with a father, a mother and a little boy.

This dad is an office worker who sits in the office all day long. It's not been a long time, it's a bit sub-healthy. So a friend recommended him to go to the square and exercise with those people. In the evening, this dad went to the square for a walk, saw some fitness equipment, but all of them are for the elderly to exercise, think that he is only thirty or forty years old, to massage the back, pedal the bicycle is a little too early; look at those who dance square dance, most of them are aunts, and they can't pull their faces to dance together; there are also ballroom dancers, and suddenly a little excited, but think that there is no dance partner, and it is estimated that my mother will not let me dance, so my father gave up. Finally, Dad saw a few people practicing Tai Chi Sword, and when he saw this line,

"By the way, do you know what a Tai Chi Sword is?" Qi Binxuan asked the little boy.

"I don't know. Feng Hao returned honestly. At this time, Luo Hongyi was also interested when he heard the Taiji Sword, and he also put down the work in his hand, moved a stool and sat down to listen.

"Tai Chi Sword, this is the quintessence of the country. According to legend, it is a martial art invented by Zhang Sanfeng of Wudang Mountain. It is a kind of martial art that holds a sword and draws circles there. Like Tai Chi, the emphasis is on four or two thousand catties. Legend has it that the essence of this martial art is that the more you forget, the stronger your skills will be. When you forget it completely, it will be the Dacheng realm. Qi Binxuan said seriously.

Luo Hongyi interjected at this time: "Then it's okay not to learn for a long time, it's the same as forgetting, isn't this a big deal?"

Qi Binxuan thought for a while, and then said: "I think there is still a difference between this, for example, when eating, you should pay attention to how to hold chopsticks when you study at the beginning, and then open your mouth when you are almost to your mouth." And after becoming proficient, these basic steps are forgotten and become instinctive. If you don't say it or leave, it's basically like forgetting everything. This Tai Chi sword should also be the same truth, I started to learn, and then I forgot it, it became instinct, when the enemy made a move, and then instinctively blocked, four or two dialed a thousand catties to offset him, this is Dacheng. ”

Seeing Feng Hao and Luo Hongyi nodding there, as if they were quite approving, Qi Binxuan wiped the cold sweat on his forehead, and said in his heart that this serious nonsense is really not easy. Then he said, "Then let's move on to the story." ”

So Dad decided to practice this. But there was no sword, so Dad got a branch in the grove next to him and practiced with him. Not to mention, the effect is not bad under exercise, and I feel much more comfortable. But this old man practiced with branches, and the other aunts and uncles who practiced Tai Chi Sword stopped doing it. They said you should take the sword so well, it's too childish to practice with a branch like this. What do people passing by think, a group of people practice swords, and one of them is holding a branch, isn't this funny, it's too low-style. Dad hurriedly promised to go back and buy a sword.

When I went back to my wallet, my father found that his pocket money was too small, and it was basically not enough to buy a sword. Because my father, like other fathers, paid my salary after getting married. Just leave some pocket money for everyday use. Then he told his mother to take some money to buy a Tai Chi sword. Then my mother said, that's not good, you don't know how expensive firewood, rice, oil and salt are, you see how much this is, how much is that, which doesn't cost money, I don't have money to buy that imported lipstick, how can I have spare money to buy a sword.

At this time, Feng Hao said with the same feeling: "Yes, my mother is too, she is buying clothes, cosmetics and bags, eating and drinking all day long, and she has to spend money to lose weight when she gets fat." My dad usually had to save pocket money to buy a cigarette. ”

Qi Binxuan agreed: "Therefore, after marriage, it is very important for a man to save some private money." Xiao Hao, you must remember this. ”

"Yes. Feng Hao agreed seriously.