ΣLemmory
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Remember every formula.Know when to use it.

Flashcards with spaced repetition, built for competition math. Teachers assign the formulas they teach, students spend five minutes a day, and each formula returns right before it's forgotten.

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RecallAlgebra

AM-GM Inequality

For nonnegative reals a,ba, b; equality when a=ba = b.

a+b2≥\displaystyle \frac{a+b}{2} \ge

310 formulas from AMC 8 to AIME that we can test you on

  • Algebra

    65

    Vieta's Formulas

    r1+r2=−bar_1 + r_2 = -\tfrac{b}{a}

  • Geometry

    82

    Power of a Point

    PA⋅PB=PC⋅PDPA \cdot PB = PC \cdot PD

  • Trigonometry

    32

    Law of Cosines

    c2=a2+b2−2abcos⁡Cc^2 = a^2 + b^2 - 2ab\cos C

  • Number Theory

    47

    Legendre's Formula

    νp(n!)=∑i≥1⌊npi⌋\nu_p(n!) = \sum_{i \ge 1} \left\lfloor \tfrac{n}{p^i} \right\rfloor

  • Combinatorics

    37

    Stars and Bars

    (n+k−1k−1)\binom{n+k-1}{k-1}

  • Probability

    28

    Bayes' Theorem

    P(A∣B)=P(B∣A) P(A)P(B)P(A \mid B) = \tfrac{P(B \mid A)\,P(A)}{P(B)}

  • Calculus

    19

    Power Rule

    ddx xn=nxn−1\tfrac{d}{dx}\, x^n = n x^{n-1}

  • See the formula bank

    Open it in the demo

A student seen from behind, working late at a desk under a lamp, with a calendar and sticky notes on the wall

Right now, no one actively helps you put formulas into your long-term memory.

  1. 1

    Formulas fade

    Forgotten within 1-2 weeks without specific practice.

  2. 2

    Classes move on

    A class learns a formula, then jumps straight into the next topic.

  3. 3

    Sources are scattered across the internet

    AoPS Wiki, random PDFs, forum posts.

Every formula a student learns should still be there on contest day.

We make review part of the course, so every student keeps what they're taught, not just the ones with perfect study habits.

A look inside

Real screens from the app. The demo has all of them, with a sample class you can click around.

Student home page: 9 cards today with a Start button, a list of formulas to focus on, and the class leaderboard
One button a day. Students see how many cards are due, the formulas they keep missing, and where they stand on the class leaderboard.

Five minutes a day.The scheduling is automatic.

    • Vieta's Formulas Assigned
    • Power of a Point Assigned
    • Stars and Bars Assign

    1. The teacher assigns

    Keep teaching your own curriculum. Each week, assign the formulas you covered, and they go into every student's deck.

  2. Recall

    r1+r2=r_1 + r_2 =−ba-\tfrac{b}{a}

    Correct

    2. Students review daily

    A few minutes a day: type each formula from memory, then, once it sticks, use it on real problems.

  3. Vieta's Formulas

    Next review

    in 14 days

    3. It comes back on time

    Each card returns right before it would be forgotten.

Then the scheduler takes over

Each right answer pushes the next review further out. A miss stays in that day's review until it's right, then the card comes back sooner. Here is one formula, where each square is a day:

  1. 0
  4. 3
  5. 4
  8. 7
  22. 21
  79. 78

5 reviews in 78 days. The gaps keep growing.

Learned in classRecallProblemMissed

Built on how memory actually works

25%50%75%100%ClassDay 10Day 20Day 30Day 40No reviewWith Lemmory reviews
Illustration using the FSRS forgetting curve. Dots mark reviews; each one makes the next decline slower.

See it for yourself

Do a review as a student, then switch to the teacher view and watch your results show up.

Ready for your own class? Start a free trial

Open the live demo