Sum of internal angles of triangle

Big secret rate

Audio graphics

Talk about chickens and rabbits in the same cage

The mystery of positioning

Second, positive and negative reactions.

Same and different

induction and deduction

Accuracy and error

Change and invariability

Third, think skillfully.

Butterfly on the ellipse

Where is infinity?

Draw line segments with compasses

Pedro's rusty compasses

Contribution of self-taught youth

Fourth, shine on you

Ants in the circle

A point in a triangle.

Great and strange

fixed point

Fifth, the topic is being done.

Mathematics of washing clothes

Brick accumulation problem

If the earth is an empty shell

Underground high-speed train

Sixth, see the micro-knowledge

Pearls and seeds

Tangent line of parabola

Infinitesimal is the ghost of quantity?

Limit concept: rigorous but difficult to understand

Can a derivative be defined without the concept of limit?

A preliminary study on the new definition of derivative

Taylor formula is easy to obtain.

Reflection after success

Parabolic arcuate area

Basic theorem of area fraction