Prehistoric I was pinched out by Nuwa

Factors, multipliers, commutative property of multiplication.

These are the beginning, Li Yang will naturally talk about multiplication and expansion.

"You have already understood these single-digit multiplications, and the next step is multi-digit multiplication! For example, what is 13x14 equal to?"

According to the definition of multiplication, it should be calculated one by one.

If the word count is too large, it will be too troublesome.

Therefore, double-digit multiplication must be regular.

Fuxi in Wa Palace, he also listened carefully, wanting to know what laws Li Yang had.

"Everything basically has traces to follow, and so do algorithms!"

Li Yang didn't talk about the so-called traces of everything, which will involve observing the sky above and understanding geography below.

It's too professional and beyond the scope of Li Yang's knowledge.

Anyway, he couldn't see whether it will rain the next day from today, in his previous life he always watched the weather forecast, and the 'grandmother' on his mobile phone was updated in real time!

"Double digits are divided into tens digits and single digits. You need to keep in mind that if it is a three digit number, it will be recorded as a hundred digit and so on!"

The second child, Xia An and the others kept it in their hearts, and when the eldest brother gave the definition, they just remembered it.

"Before multiplying double digits, there is one more thing to learn!"

Wa Palace, Fuxi frowned slightly, with his calm mind, he also wanted to shoot people.

But he didn't move. Before he talked about multiplying double digits last time, he said that the decimal system brought a lot of merit, but this time he wants to see it.

Can this human Li Yang still attract merit?

Li Yang doesn't show off in front of his clansmen.

"Before multiplying double numbers, have you ever thought about multiplying odd numbers by even numbers..."

Speaking of this, Li Yang frowned!

He doesn't seem to have talked about singular numbers, what are even numbers, what are three-digit numbers and four-digit numbers?

"Do you know what odd and even numbers are?"

"I know, brother! You've said it before, two numbers are double digits, and one is odd number!"

The second child raised his hand, he had heard it from the elder brother.

However, the eldest brother did not tell them in detail.

Li Yang shook his head, he was negligent again.

"You guys are fine. A number, such as '1', is an odd number! '11' is a double-digit number.

'111' is a three-digit number, '1111' is..."

"Four digits!"

The second child raises his hand, he will be strong.

"Yes! The following digits can be deduced in the same way!"

There should be no definition in these mathematics, right?

Li Yang murmured in his heart, he was not particularly good at mathematics.

After all, the mathematics of liberal arts students seems to be different from that of science students?

"Before I talk about double digits, let me tell you about multiplying odd numbers by double digits!"

"Before I divided the double digits into single digits and tens digits!"

"Odd numbers are numbers!"

"Like '2' x '12'!"

Li Yang wrote this formula on the ground with a tree branch, and marked 'single number' and 'even number' under '2' and '12' respectively!

"When they are multiplied, they can actually be divided into '2'x'(10+2)'!"

When Li Yang said this, he looked up and saw the second child, Xia An and the others, with a somewhat confused face.

"I ask you how much 10+2=?"

"12 Ah!"

"Isn't 12 just (10+2)?"

“大哥，我们知道12=10+2，还知道它是6+6、3+9……只是‘（）’这是啥？”

"???"

Li Yang raised his forehead, careless.

Originally, I just wanted to say something briefly, but later I thought it would be better to add some details!

Now, some painted tigers are not anti-dogs!

He shouldn't have separated '12', it could have been calculated, why do it in the opposite direction?

This is asking for trouble!

Directly speaking, multiply the single digit and the tens digit by multiplying the single digit and the tens digit respectively, and then add them together!

Just let them remember the rules!

And now...

Parentheses are also involved, but we will still use parentheses in the future, so it’s okay to talk about them first at this time.

"It's called parentheses, and its function is to change the order of operations!"

"Remember its function! In the four arithmetic operations, addition, subtraction, multiplication and division appear in one operation at the same time. If you calculate addition and subtraction first and then multiplication and division, you need to add parentheses! For example, 1+2x3, then it must be on 1+2 Add parentheses and turn them into something like (1+2)x3!"

Li Yang was heartbroken while speaking.

Because of the brackets, he thought of complex formulas in the four arithmetic operations.

Forget it, take your time!

He doesn't even teach division now!

It is still early to talk about the use of parentheses in four-diamond calculations.

"Remember a rule, the rule of multiplying odd numbers by double digits..."

Li Yang stopped messing around with the mysterious operation, and honestly finished the multiplication of odd numbers and double digits.

After speaking, he ordered Xia An's name.

"Calculate how much 3x12 equals!"

Xia An muttered words as he slid his fingers on the ground.

"Multiple an odd number by an even number, first multiply the ones digit, then multiply the tens digit, and finally add the two results... I see, it is equal to 36!"

"Brother, am I right?"

There was excitement on Xia An's face.

These numbers are not just numbers, they are very practical in life!

"That's right!"

"Second, you can do the math too, um... 4x13!"

The second finger also slid on the ground.

The same is writing numbers.

Xia An's writing was written by Li Yang, who could understand a little bit, but the second child's writing was like a divine book, which he couldn't understand.

"Brother, it's 52!"

The traces on the ground were crowded together, Li Yang couldn't see how the second child could calculate the correct answer.

Li Yang didn't confirm in time, which made the second child feel a little uneasy.

Could it be that I made a mistake?

"Well, it's 52!"

The second brother breathed a sigh of relief, yes.

"I won't ask any questions about multiplying even numbers by odd numbers. Let's continue with the teaching later, multiplying double digits and multiplying multiple digits!"

"Just now I asked you to multiply single digits by double digits. It is single digits multiplied by ones digits and then multiplied by tens digits. What about double digits?"

The second child, Xia An and the others fell into deep thought.

Double-digit multiplication should also be split, right?

"Brother, should we still split?"

Xia An randomly wrote two numbers on the ground, '12x13'.

According to the previous algorithm, the ones digit is multiplied by the ones digit and then multiplied by the tens digit...

Can there be an extra tens?

Xia An frowned, how to multiply the remaining ten digits?

Several people thought for a long time, shaking their heads to no avail.

"Same as before, split and multiply! But here involves a cross multiplication..."

Wa Palace, Fuxi frowned again.

What cross multiplication?

Thinking of single digits is so troublesome?

While Fuxi was thinking, Li Yang had already briefly explained the method of cross multiplication.

Fuxi came back to his senses, listened again, and found out what Li Yang said about multiplying the ones digit by the ones digit and then multiplying the tens digit, and then multiplying the tens digit by the ones digit and multiplying the tens digit.

He can't understand!

Fu Xi frowned.

What was the cross multiplication just now, why didn't I understand it later?

Fuxi looked down, if he didn't believe in evil, he would not be able to understand it!

After teaching 'Cross Multiplication', Li Yangrang asked again.

This time it's the second child.

"You calculate how much 12x24=!"

The second child bowed his head and began to click on the ground with his fingers.

But in Wa Palace, Fuxi frowned to count.

How should I calculate this?