"Is there any treasure behind this?" Xiao Yan slowly wiped off the dust covering this geometric pattern with a fountain pen, while wondering in his heart.

After a while, a figure more than one person tall appeared in front of Xiao Yan, similar to a simple house. The roof of the house is made up of an isosceles triangle, the body of the house is composed of a square, and the foundation of the house is a rectangle, just like such a cross-section, like a geometric figure.

"Big brother said that once this kind of strange place appears, where there are geometric shapes, there must be a simple cave sealed behind it, you only need to calculate the area of these geometric figures, and then attack it, you can unlock it, behind this figure, there is really a cave?" Xiao Yan muttered to himself.

"Senior Brother Xiao Yan, hello, what are you doing?" While Xiao Yan was thinking, Ruolan had already solved the Heavenly Demon outside, and then she saw Xiao Yan standing in front of the inner wall of the cave at a glance, and with a surprise, Ruolan quickly ran over.

"Huh, what is this?" Ruolan came quickly, and at a glance saw the geometric pattern on the wall.

"Sister Ruolan, there must be some treasures in this, this pattern is the seal that seals the space behind this wall, we only need to calculate the area of these patterns, and then we can open it, I can't imagine that if we find a hole at random, there will be such a place, there may be high-level reading notes or high-level cultivation magic weapons in it. Xiao Yan didn't hide anything and said directly to Ruolan that if it was Xiao Ming, Xiao Yan wouldn't tell Xiao Ming.

"Ah...... Baby!?" Ruolan was also taken aback when she heard Xiao Yan say this, and her eyes widened.

"Huh...... Thought of it. Xiao Yan looked at Ruolan, and then looked at Xiao Ming, who was still recovering in the distance, and suddenly thought about it.

"Sister Ruolan, there is a baby behind here, you stand behind me, I just understood the area formula of these figures a few days ago, and now it comes in handy. Xiao Yan turned his head to Ruolan and said solemnly, and then, his eyes glanced at Xiao Ming, who was sitting cross-legged.

"I can't think of the endless road of heaven, Xiao Ming, don't blame me for taking Ruolan away. Xiao Yan turned his head, and a smile appeared on the corner of his mouth.

"Ah...... Slow down, Senior Brother Xiao Yan, Brother Xiao Ming is still recovering, you won't have a problem unlocking this seal. But Ruolan suddenly thought of Xiao Ming, and hurriedly stood in front of Xiao Yan to stop Xiao Yan.

"Sister Ruolan, it's okay, this is just a seal, there is no big movement after unlocking, and it won't make any noise to Xiao Ming. Xiao Yan smiled slightly, but there was a trace of cunning in the depths of his eyes.

"Oh, that's it, that's okay, Senior Brother Xiao Yan, you can calculate it quickly. Ruolan also immediately believed Xiao Yan's words, and then got out of the way.

"Rub the ......" and Xiao Yan also took out a finger-length ruler from his schoolbag when Ruolan got out of the way, and Xiao Yan held it steadily.

"Sister Ruolan, now to calculate the area of this figure, we first have to measure their side lengths, I will measure them here, Sister Ruolan will count them for me. Xiao Yan took the ruler and stepped forward.

"Well, okay, Senior Brother Xiao Yan. ”

Ruolan nodded.

"Go!" Xiao Yan walked a meter in front of this pattern, threw his ruler forward, Xiao Yan's index finger and middle finger together, a ray of light shot out from his fingers together, and then the light shrouded directly on the ruler in the air, the light shone on this ruler, and suddenly the ruler of the finger length became longer rapidly at a speed visible to the naked eye, and finally became a ruler more than one meter long, and the next moment, Xiao Yan remotely controlled the ruler and moved closer to the edge of the triangle.

This ruler is also a magic weapon, and if ordinary people or people below the third grade get it, it is useless at all. Rulers, compasses, triangles and other geometric utensils all require users to have a strong internal force foundation, and the Chinese characters and ancient poems in the body have not accumulated to a certain extent, and they cannot drive the action of the ruler at all. Only with a strong internal force can it drive the moving ruler triangle to become bigger and smaller, and so on.

Generally speaking, it is not until the third year or above that cultivators slowly use the magic weapons of fountain pens, rulers, and triangles. Moreover, the circumference of the square, the circumference of the triangle, the area, etc., are all profound meanings that can only be learned after the third grade, if Xiao Ming had discovered this pattern before, there would be no way to break the seal.

It's just that Xiao Yan just mastered the side length and area formula of this pattern now, but now it just comes in handy. But before that, Xiao Yan had to measure the side lengths of these geometric figures.

"Sister Ruolan, remember that the side length of this triangle is 50, 50, 80 cm, the side length of this square is also 80 cm, and the length of the rectangle is 100 cm and the width is 30 cm. Xiao Yan manipulated his ruler and slowly leaned against the line segment of the geometric figure, and quickly measured the side length of the geometric pattern.

"When ......" The ruler regained its size and returned to Xiao Yan's hands. This measurement also consumed Xiao Yan's internal force.

"Did you write it down? Sister Ruolan. Xiao Yan put away the ruler and looked back at Ruolan.

"Well, I wrote it down, Senior Brother Xiao Yan. How do you calculate it next?" Ruolan's cultivation was only in the middle of the third grade, and she hadn't studied the ruler and triangle yet, so now she naturally set her sights on Xiao Yan.

"Next, it's up to Senior Brother Xiao Yan. Xiao Yan enjoyed Ruolan very much, looking at her gaze with a hint of envy, and patted her chest with her palm, looking very happy. Sure enough, without Xiao Ming, Ruolan would have focused on him.

"This is the area formula of the rectangle and the square, the length of their sides, just add up, Sister Ruolan, while I am calculating, you also happen to understand it at the same time......" Xiao Yan squatted down, a pen and scratch paper appeared in his hand, and began to write and draw on the scratch paper.

"Hmm...... I listened. Ruolan also knew that Xiao Yan was teaching him knowledge, and she looked very serious, after all, she had just made up her mind to work harder to become stronger, not to be Xiao Ming's brother's oil bottle, and now that Xiao Yan taught her cultivation experience, Ruolan naturally had a very serious expression.

"Now, we only need to add up the length of the three sides of the triangle, you see, 50 + 50 + 80 = 180, 180 cm, exactly the perimeter of the triangle, similarly, we can also use multiplication, if the triangle is an equilateral triangle, his base is also 50, we only need to know one of its sides, know one side, we only need to use 50 * 3, we can also calculate the perimeter of the triangle, the triangle is also divided into isosceles triangle, obtuse triangle, right triangle ......" Seeing Ruolan listening to herself carefully, Xiao Yan suddenly felt full of enthusiasm and explained to Ruolan in more detail.

The reason why Ruolan was able to be promoted to innate within twenty days was inseparable from Xiao Yan's guidance. Xiao Yan's teaching seems to have returned to the days when he and Ruolan were alone for more than 20 days.

"Oh, I see. Ruolan is naturally not stupid, Xiao Yan gave such a guide, Ruolan also quickly understood the calculation of the perimeter of a triangle, the perimeter calculation method of a square and a rectangle.

"Well, now because these figures are connected, we calculated their respective perimeters, but to subtract the parts they are connected, 180 + 320 + 260 - 160 = 600, this is exactly the perimeter of this geometric figure we calculated. Xiao Yan unknowingly, on the way to teach Ruolan, he had already solved the perimeter of this geometric figure.

"Ah, it turns out that this is still needed, hehe, Senior Brother Xiao Yan, you are really powerful. When Ruolan heard Xiao Yan say this, her eyes suddenly lit up again.

"Hehe, my eldest brother said, when solving the seals of these geometric figures, you have to combine it with reality and know how to be flexible, if Sister Lan is so perceptive, this is nothing. Xiao Yan was praised by Ruolan, although he still had a faint smile on his face, his heart had already blossomed.

"Now, the perimeter has been calculated, we have to calculate the area, the area formula of this rectangle and square is the side length multiplied by the side length, it is very simple, even if we go back to school, Teacher Liu will teach us. But now the slightly more difficult thing is the area of this isosceles triangle, which we only know the length of its sides, not its height, and we have to calculate the area...... It was very difficult for the two of us in the third grade. Then, Xiao Yan quickly calculated the area of the rectangle and the square, but in the face of the area of the triangle, he was a little difficult.

Because, the area formula of a triangle has to be taught in the fourth grade.

Although Xiao Yan had already received tutoring from his junior high school student's eldest brother in the fourth and even fifth grades before he came, it was still very difficult for Xiao Yan.

Especially now this triangular area is like a roadblock in front of Xiao Yan. When he calculated the area of the triangle, Xiao Yan realized that he seemed to be happy too early.

"What's wrong, Senior Brother Xiao Yan, what's wrong with the area of the triangle?" Ruolan was fascinated by what she heard, but she didn't expect Xiao Yan to suddenly break off.

"The area formula of this triangle was only able to be understood by the fourth grade, but my eldest brother told me that it is the base multiplied height divided by 2, but now we have only measured the side length of the triangle, and the height of this triangle, I seem to have forgotten to measure it. Moreover, without a triangle, even if the height of the triangle is measured, it is not very accurate......" Xiao Yan felt that he blushed a little, and he would forget such an important issue.

"Ah...... Then, what should I do? If that's the case, wouldn't it be impossible to break this seal?" Ruolan was taken aback, her interest had been mobilized by Xiao Yan, and now that she couldn't unlock the last step, Ruolan's heart was a little uncomfortable like a cat's claw.

"Uh...... This, I seem to remember, my eldest brother once said that the height of an isosceles triangle is the midline of the bottom, and you only need to find the midline and then use the Pythagorean theorem to find the high...... However, what is this midline, this Pythagorean theorem, the eldest brother also said, it seems that it is not something that we can understand now. Xiao Yan's forehead was wrinkled into a Sichuan character, and he was a little disappointed when he looked at Ruolan, and he was even a little ashamed.

"Ah...... But now it's the last step, are you going to give up?" Ruolan was a little disappointed.

"The solution is yes, we now have to calculate the area of the triangle, we can only use a ruler to try to measure its height again, a few more tries, maybe we can calculate the correct one. Xiao Yan looked at the damn triangle on the wall with some uncertainty, and then looked at Xiao Ming, who was sitting cross-legged and cultivating over there, and a trace of unwillingness flashed in his eyes.

If he can't solve the area of the triangle, he won't be able to go treasure hunting with Ruolan, and he will have to take Xiao Ming with him in the future.