K–12 Mathematics · Proof-first

Mathematics, understood.
Not memorized.

理解数学,而非背诵公式

Every formula here is guessed, discovered, proved, and taught back — by the learner. From Grade 5 arithmetic to Grade 12 calculus, nothing is asserted without a reason you can follow.

FIG. 1 — SHEAR A PARALLELOGRAMA = bh = 24, always
h = 4b = 6
shearslant = 4.47
Drag the slider. The sides stretch — the area refuses to move. That refusal is the theorem.
The Method · 数学家的思维方式

Five moves of a mathematician

i.

Guess first

先猜再算

Commit to an intuition before any computation. The answer is never revealed before you commit.

ii.

Discover

动手发现

Drag a figure until an invariant refuses to move. You see the rule before it is named.

iii.

Prove it

一题多证

One fact, many proofs — each tagged with the thinking move it trains. Methods are peers, not steps.

iv.

Generalize

举一反三

Find the one move that cracks a whole family of shapes, and see where every idea descends from.

v.

Teach it back

讲给别人听

Close each concept by assembling the explanation in your own words. If you can teach it, you own it.

Rigor · 严谨

An approximation is never passed off as an identity.

A circular sector is an arc, not a triangle. An unrolled ring is a trapezoid, not a rectangle. Where a limit is required, we say so — in words a curious ten-year-old can follow.

Measuring checks one case. Proof guarantees all of them, forever.

THEOREM 5.5.1GRADE 5 · GEOMETRY

The area of a parallelogram with base b and height h is A = bh.

Proof (cut & rearrange). Cut the right triangle off one end and slide it to the other. Nothing is created or destroyed; the figure is now a rectangle of sides b and h.
One of four proofs on this platform — each trains a different thinking move.