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blackpenredpen

Sharing the fun of solving math problems!

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2420 videos

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Finding the "volume" of a 4d sphere

38K views
2 weeks ago

My first triple improper integral via spherical coordinates

29K views
2 weeks ago

This calculus proof is only for math majors (National Taiwan University entrance exam)

12K views
3 weeks ago

Is x! = 0 solvable?

34K views
3 weeks ago

Volume of revolution (single integral vs triple integral)

12K views
3 weeks ago

A lovely calculus proof problem! (National Taiwan University entrance exam)

15K views
1 month ago

How math majors use the intermediate value theorem!

34K views
1 month ago

Brilliant minimum problem

14K views
1 month ago

So you want the Gaussian integral trick again?

17K views
1 month ago

Why do mathematicians think disc=square?

14K views
2 months ago

How to welcome a math Phd friend at the airport

31K views
2 months ago

How to rigorously prove that a limit is WRONG!

20K views
2 months ago

Can f'(x)=f^-1(x)?

71K views
3 months ago

Simple limit but most students cannot prove it!

16K views
3 months ago

How to find a delta for a specific epsilon (epsilon-delta definition of a limit)

6.6K views
3 months ago

How to find a formula for delta (epsilon-delta definition of a limit)

18K views
3 months ago

Brilliant Trig Identity Challenge!

15K views
4 months ago

It’s not joke, it’s rigorous enough for physics… 😂

167K views
5 months ago

My first abstract algebra problem in 14 years!

101K views
5 months ago

Why are integrals so hard?

26K views
5 months ago

I’m sorry, I have been saying “let x=1” wrong for 13 years

119K views
5 months ago

95K views
6 months ago

How many square roots does the 2x2 zero matrix have?

26K views
6 months ago

Calculus students don’t use these inequalities anymore!

27K views
6 months ago

Factoring a trinomial (what I learned in Taiwan vs in US)

52K views
6 months ago

Here's how I would solve this high school math question without calculus (finding extrema of trig)

16K views
6 months ago

Believe in Cauchy–Schwarz Inequality, NOT calculus 3

46K views
7 months ago

Sum of n/2^n*cos(n*pi/3) using complex numbers

20K views
7 months ago

If 1+z+z^2+z^3+z^4+z^5+z^6=0, then z+z^2+z^4=?

46K views
7 months ago

51K views
7 months ago

A fancier way to solve this radical equation

18K views
7 months ago

A taste of "when there are no numbers in math"

16K views
8 months ago

Believe in calculus, NOT pictures!

17K views
8 months ago

100 integrals (remake + solutions) full collection on Patreon

13K views
9 months ago

Big Brilliant Integral

23K views
9 months ago

What Integration Technique Do I Use? Q1 to Q5 (trig sub, u sub, DI method, partial fraction) calc 2

15K views
9 months ago

The last virtual office hour! (Chegg Trig & Precalculus)

6.6K views
9 months ago

The coolest way to solve an equation!

81K views
9 months ago

65K views
10 months ago

All solutions to x^2=2^x (remake+notes)

58K views
10 months ago

A quick guide to finding the range of a fuction! Chegg Trig & Precalculus office hour

6K views
10 months ago

Cubic vertex formula (no calculus)

14K views
10 months ago

Are they the same function? Be careful with the domain! Chegg Trig/Precalculus office hour

7.4K views
10 months ago

Making a cubic equation have a double root

17K views
10 months ago

5 Math Video Categories That Grew My Channel (12 Years on YouTube)

13K views
10 months ago

How to solve logarithmic equations! Chegg Trig & Precalculus Office Hours with blackpenredpen

8K views
10 months ago

My first x^x congruence: x^x≡2 (mod5)

38K views
10 months ago

Let's solve exponential equations! Chegg Trig & Precalculus Office Hour!

8.6K views
11 months ago

How to solve HARD polynomial equations! Chegg Trig & Precalculus Office Hours

10K views
11 months ago

Can d^2y/dx^2=(dy/dx)^2?

94K views
11 months ago

sin(x)+cos(x)=? Vertical asymptote vs hole? Inverse of (ax+b)/(cx+d)=? Chegg Precalculus office hour

8.5K views
11 months ago

The last question from the Berkeley mini Math Tournament (for 8th graders)

21K views
11 months ago

Which is bigger: a^3+b^3 or c^3?

21K views
11 months ago

Be careful when you use the law of sines! What's sin(18 deg)? & more! Chegg Precalculus Office Hours

8.2K views
11 months ago

"Dear Bprp, I have a pretty unusual question": If sqrt(a+sqrt(a+sqrt(a)))=128, then floor(a)=?

58K views
11 months ago

100 precalculus equations & inequalities (in one take)

60K views
11 months ago

How to solve a tricky domain problem and more? Chegg Trig & Precalculus Office Hours

7.5K views
11 months ago

"This fully tests your understanding of calc 1 differentiation & integration" Cambridge STEP 1 exam

19K views
11 months ago

Ask me Trig! How do you solve tricky trigonometric identity problems? (Chegg Virtual Office Hours)

9.7K views
1 year ago

This is how they asked complex number problems on the 2023 AS-Level further maths paper

20K views
1 year ago

Trig & Precalculus Office Hours w/ @blackpenredpen - We're Live, Ask Away!

8.1K views
1 year ago

This equation looks werid

57K views
1 year ago

Can we solve this square root equation?

39K views
1 year ago

A cubic formula that you probably haven't seen before!

26K views
1 year ago

I want a simple life, but WolframAlpha doesn't allow it!

46K views
1 year ago

If x^y=8 and x is bigger than 1, then what's the minimum of x+y=?

38K views
1 year ago

Pell's equation (Introduction & example) ft. @octopuskeng

24K views
1 year ago

Integral battle! 2024 vs 2025

34K views
1 year ago

You probably haven't solved a quartic equation like this before!

67K views
1 year ago

Finding the BIGGEST rectangle under y=x^3 (but NO calculus!)

66K views
1 year ago

They didn't get this right! Berkeley math tournament integral bee

12K views
1 year ago

Proving the angle sum identity for sine and cosine

65K views
1 year ago

Believe in triangles, NOT squaring both sides!

92K views
1 year ago

They didn't get this integral right, so here's the solution (Berkeley Math Tournament Integral bee)

118K views
1 year ago

Hello from UC Berkeley (Berkeley Math Tournament Day)

9K views
1 year ago

Finding the domain of x^x

33K views
1 year ago

Math for fun: solving (4^x+8)^4-(8^x-4)^4=(4+8^x+4^x)^4

18K views
1 year ago

453K views
1 year ago

You don't need calculus for this question

33K views
1 year ago

Live: This is what the 2023 Berkeley Math Tournament calculus test looks like!

15K views
1 year ago

Can you solve these 3 calculus tiebreakers the fastest? (2023 Berkeley Math Tournament)

33K views
1 year ago

A non-real way of solving Fresnel's integrals (but I am not sure if it's legit)

19K views
1 year ago

What if we changed a Fresnel's integral?

35K views
1 year ago

In how many ways can we distribute 6 distinct balls into 3 identical boxes?

22K views
1 year ago

Solving improper integrals without actually solving them! (part 1)

20K views
1 year ago

Limit of ln(x)/W(x) as x approaches infinity (Lambert W function)

69K views
1 year ago

I used a double integral to solve a single improper integral

42K views
1 year ago

This limit has 0^0 indeterminate form but the answer is 0

26K views
1 year ago

How Cauchy would find the maximum of sqrt(x)+sqrt(y)

59K views
1 year ago

What is the equation of the line that’s equal-distance from two given points?

16K views
1 year ago

Is x^x=0 solvable?

558K views
1 year ago

Which equation has no real solution: e^x=2, e^e^x=2, or e^e^e^x=2?

69K views
1 year ago

3 levels of "perpendicular"

46K views
1 year ago

Finding the distance from a point to a line (using vectors)

44K views
1 year ago

When you accidentally multiply matrices the wrong way, but nobody notices (Reddit r/mathmemes)

179K views
1 year ago

Can we use power series for this limit of a two-variable function?

18K views
1 year ago

What is f''(x) in terms of dx/dy?

30K views
1 year ago

Quadratic formula but (a, b, c) goes to (0, 0, 0)

55K views
1 year ago

The most fun way of solving this quartic equation

44K views
1 year ago

Quadratic formula for non-constant coefficients

92K views
1 year ago

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