r/learnmath

Definition of a Trapezoid

This may sound a bit stupid, but what is the exact definition of a trapezoid? Is it a quadrilateral with EXACTLY one pair of parallel sides or aquadrilateral with AT LEAST one pair of parallel sides? My teacher says it's the first one, but my own textbook (Art of Problem Solving: Geometry) says it's the latter.

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u/brothor12 — 10 hours ago

Someone explain me Dijkstra's algorithm and its fundamentals

I recently attended my college lecture and I was literally told to memorize the algorithm which I couldnt. It would be nice if someone could explain me the algorithm as in from a fundamental apporach

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u/CrImSoNbOneSHAker — 16 hours ago

Need Help Understanding this Basic Combinatorial Problem

This example is from “A First Course in Probability 6E” by Sheldon Ross:

A class in probability theory consists of 6 men and 4 women. An examination is given, and the students are ranked according to their performance. Assume that no two students obtain the same score.

If the men are ranked just among themselves and the women just among themselves, how many different rankings are possible?
Solution:
(b) Since there are 6! possible rankings of the men among themselves and 4! possible rankings of the women among themselves, it follows from the basic principle that there are (6!)(4!) = (720)(24) = 17,280 possible rankings in this case.

I am having a hard time visualising this example. If it had a factor of 2 multiplied in the solution, I can understand that the rankings would mean [Men rankings][Women rankings] or [Women rankings][Men ranking]. But that’s not the case here.

How would a ranking look like in this example?

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u/Gay-Berry — 15 hours ago
▲ 1 r/learnmath+1 crossposts

[Online] Math Tutor | Algebra → Calculus BC | SAT Math | College Math (DIff eq, Multi Calc & Linear Algebra)

Hi! I'm a math major student at a top-20 university offering 1:1 online math tutoring.

Subjects I cover:

  • Algebra 1 & 2
  • Geometry & Trigonometry
  • General Math
  • Pre-Calculus
  • AP Calculus AB & BC
  • SAT Math
  • Multivariable Calculus
  • Linear Algebra
  • Differential Equations

I have more than 3 years of experience. I love to build real understanding, not just drill formulas. I love to explain problems in the most approachable way.

I can help with homework and test preparations with flexible timing.

ps. Both English and Chinese work for me.

Rate: $45–75/hr, depending on subject, flexible on frequency. In the first session, we'll assess where you are and what you need.

DM me if you're interested or have any questions!

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u/Zestyclose-Reply4674 — 18 hours ago

i want to learn mathematics i am biologist

hi my name is Abdallah and i want to learn mathematics i love space and i think if i learned math well i can understand some theories and formulas of Einstein and Maxwell

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u/Electrical_Side2144 — 17 hours ago

Genuinely what is the point of secant, cosecant, and cotangent?

So I know that cosecant is 1/sine, secant is 1/cosine, and cotangent is 1/tangent. This is all seems extremely redundant to me and next to useless. I am aware of the geometric reasoning of cosecant and secant. But even that, I don't feel like justifies the need to create 3 new functions for use. So, is there a good reason?

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u/Inevitable-Ad2579 — 1 day ago

I have a problem with my degree exams

Hi, I am a degree math student and I am struggling with passing my exams.

It's not that I don't study, or anything like that (I study a ton and learn the material perfectly), but when the exam comes around, my abilities suddenly plummet.

To give an example, yesterday I took a theoretical-practical analysis exam and I messed up very stupidly in each of the parts.

In the theoretical part I was doing the proof they asked me for and at one point you took two points x, y from a closed interval and you had to use the fact that their difference was zero, which you could do simply by saying that x = y.

Well, for some reason, my brain couldn't grasp that it could be like that at the time, and I went in a completely different direction, which wasn't right. Anyway, I messed up stupidly, and after the exam, I remembered what I should have written.

And then, in the practical part, I had to calculate the sum of a telescopic series, very difficult, to be honest, but I know how to calculate telescopic series, but at that moment even the initial step (decomposing into simple fractions) didn't cross my mind and then, after the examen, I was like "No way, I knew how to do this"

I've had ADHD diagnosed since I was 7, so that might have something to do with it, but I've never had big problems with it before, academically speaking, so maybe it's related with math?

What may be happening to me. Help.

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u/Space_Cucumber_User — 19 hours ago

Books to start learning mathematics

Hello everyone, I just finished high school and am going to pursue a double degree in mathematics and computer science. There is a 2-ish month gap till I start university. Are there any books that will help me bridge the gap between high school and university mathematics? My high school math course lacked quite a bit of linear algebra such as matrices, etc. If so, how would you recommend to read and practice problems. Any help would be greatly appreciated, thanks! My high school math course lacked quite a bit of linear algebra such as matrices, etc, so suggestions for linear algebra books would also be helpful!

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u/Delicious-Deer8803 — 19 hours ago

Why does division feel harder to “understand” than multiplication?

Something interesting I’ve noticed is that many students become comfortable with multiplication after enough practice, but division often still feels confusing even when they know the steps.

With multiplication, learners usually see patterns fairly quickly. Division, on the other hand, seems to create more hesitation — especially when remainders or larger numbers appear.

Sometimes it feels like students memorize the process without fully understanding what division is actually representing.

I’m curious whether others think division is conceptually harder than multiplication, or if it’s mainly the way it’s introduced early on.

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u/aditya72459 — 18 hours ago

is math really just practice?

dominant right brainer here, creative, etc, had trouble with math since HS i just never got it,

in HS i took it twice, as well as the state exam, barely passed the second time, had a tutor

coming across this same math in college, i failed my math class with D last semester, unacceptable for my career,

i'm awesome in biology in chem which is crazy right? also psych all As so what's up with math?

not to blame the educator but all my math teachers have been wackos i learned more from intelligent students around me, not sure why

i had a lot of hours tutoring in Hs in college i dont use tutors because they all teach different so i stick to my professor , my current professor has a 2 stars on rate my professor lol ,

i have my final tm, didnt do so bad, but i need a 85 to pass, im being stuck on some problems and im just curious

is math really just practice?

is there an easy way to learn math,

since math is universal what country do you think teaches math the easiest?

any tips to grasp numbers

thanks

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u/OneHomework1372 — 1 day ago

Two ways to calculate slope but different answers

Lets say i have the equation:

y=5x^2+10x+3

I want to calculate slope at a specific point, im wondering why method 1 is invalid.

Method 1: put it into y=mx+b form

y = (5x+10)x+3

now m=5x+10: it is a variable slope based on x location as expected, but the coefficient is wrong

Method 2: derivative

y'=10x+10

now m=10x+10: this is the correct answer I believe

Any help for me to understand this fundamentally woukd be much appreciated!

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u/GraniteGrape — 23 hours ago

How do I multiply?

I have Provincial Achievement Tests coming up, and I have to do a math test without calculators. Unfortunately I suck at multiplying (mainly because I'm autistic and have a harder time with stuff like that) and we have a maximum time limit of 30 mins to complete 20 questions. I struggle with multiplying a lot even tho I'm 15 and have not said anything about it until now because I'm scared I'll be made fun of for my lack of knowledge. Any tips?

note: I can do my 1-3,5,10-11 times tables if that helps

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u/Ok_Flower_1038 — 22 hours ago
▲ 1 r/learnmath+1 crossposts

Failing Math-- Am I cooked?

Soo I'm in grade 10 academic math. My math grade on my midterm report card was a 40% and i got a 41% on my midterm exam. School ends in a month, finals are yet to come, I'm terrified. I got a 30 something percent on my last test. My final is worth 30% of my grade I think but I'm nervous because I haven't been doing great all semester. Is it possible for me to still pass? My attendance is honestly really bad, I'm trying my best to improve it-- it's not that i'm necessarily bad with numeracy but I haven't been there to properly learn everything. We still have another 2 whole units. I'm soo scared for my final exam. I really want to pass. The class I'm taking right now is a pre-req, I'm worried I may have to give that up. Can I still pass or am I for sure gonna fail?

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u/sundialvillage — 22 hours ago

Linear Algebra Suggestions

I just passed Calc 2 with an A! Taking linear algebra this summer semester. Any tips or online notes I can take a look at? I have 4 weeks till my summer semester starts so trying to get ahead. Thank you in advance

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u/9-AV-4 — 22 hours ago

I dont get why we use pemdas

From what I understand, pemdas is not a rule of math, we use it for uncomplexity between people, then how do we know that the answer to 2×8+4 is 20? Like it's just order made by us, it's like I invented a rule of math that everyone would use, add 1 to everything. The equations would not be right, but that's the rules no? I dont get ittttt

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online math learning with NO videos? specifically algebra 2 to pre-calc

i straight up hate internet videos and can't watch them but so much of "online how to" is a video now. i'll take books/pdfs too if they're free/inexpensive and reasonably easy to follow in self-learning

i haven't done real math since like 2011 and i'm trying to go back to school for engineering so i wanna make sure i remember it. i got through trigonometry/pre calc in high school just fine i just wanna practice a bit again so i dont go to a calculus class like "lol whats a fraction"

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u/shinichimechazawa — 1 day ago

Why do perimeter and area get mixed up so often?

Something I’ve noticed is that many students seem comfortable using the formulas for perimeter and area during practice, but still mix them up surprisingly often in actual questions.

What’s interesting is that even after understanding the definitions, some learners still treat both ideas almost interchangeably unless the question is very direct.

I’ve always wondered whether this confusion happens because the formulas are introduced too early, or because students don’t spend enough time visualizing what perimeter and area actually represent geometrically.

Does anyone else think these two concepts are harder to separate intuitively than they first appear?

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u/aditya72459 — 1 day ago