Equation For a Circle

[ZIZERMAN25]

Thanks bro

[asiang00dies]

thanks man! i got a test tommorow and this really helped!

[nikiannb]

if you're given an equation, say x^2+y^2 = 36, how would you find, from that, one point on the circle? my teacher didn't even bother showing us this..

[AlRichards314]

@nikiannb The radius of this circle is 6 since the square root of 36 is 6. This means that every point on this circle has x coordinates between -6 and 6. So, if you want to find a specific point then replace x with a number between -6 and + 6 and solve for y. For example, if you want to find the point that has an x coordiante of x = 3, then 3^2 + y^2 = 36, 9 + y^2 = 36. Subtracting 9 from both sides we get y^2 = 27, so y = +/- root(27). Then two points on this circle are (3,+/- root(27)).

[StephenYamato]

so, can the equation have a minus sign between the x term and y term?!

[AlRichards314]

@StephenYamato If you change x^2 + y^2 = r^2 into x^2 - y^2 = r^2 it is no longer a circle. The graph becomes a curve called a hyperbola - quite different actually.

[gigglepox]

thank you man, my teacher forgot to teach us this and I have an exam tomorrow :P

[sebaseba2345]

@gigglepox what kind of teacher do u have ? wow .....

[APMathNerd]

I feel so stupid... I just spent 10 minutes trying to isolate the Y to put it as a function into my calculator... then I remembered the definition of a function... UGGGHHH

[christophbraunmuller]

what are the three dots before r=5 (between r^2=25 and r=5)??

[AlRichards314]

@christophbraunmuller Those three dots are a mathematical abbreviation for the word "therefore". So that line would be read, "Therefore r = 5".

[christophbraunmuller]

@AlRichards314 wow, never knew that! Thank you so much for responding! btw, do you know if it also works when you're doing maths in another language? Say french or german? thanks again!! Cheers! CB

[AlRichards314]

@christophbraunmuller I don't speak German or French, but math symbols are very universal, so I'd assume it should work in any language.

[christophbraunmuller]

@AlRichards314 I actually did a google search yesterday after reading your response, and found out that the first usage of this symbol was by "Johann Rahn in 1659, in the original German edition of his book Teutsche Algebra" (source wikipedia), in German!... so it must be Universal. We're always learning! Cheers! And great work you're doing on those videos btw! Thanks for uploading them! :) Cheers! CB

[AllThatRemainsFan100]

Why can't my grade 10 teacher make it this simple...

[stereolovelexx]

so in simple words use the Pathergorium theoren whatever its called and you know you did it right when the anser is the radius, and ten you just take that answer and square it to get the equation?

i don't understand why yours is so complicated? or maybe i just see it differently

[HAYHUNMON]

2:00 With Radius Awwrrr :) ahaha

THUMBS UP IF YOU KEPT PRESSING 2:00 TO HEAR AWWRR OVER AND OVER AGAIN!

[30centz]

LOOOOL THIS IS THE EXACT COURSE IM DOING IN ONTARIO, CANADA....i got sooo weirded out when I saw the 2.4 ...

[caesiume]

Canadian accents are so sexy.

[TheMysweetypie]

Better than my teacher... :)

[captainclayman]

haha i like the way you say R

[MilitantBlackGuy1]

:L 'With radius awrrr'

[robirandres]

Very helpful!

[OttomanSultan123]

lol my teacher sent me here

[milan3112]

thanks so much for the explenation

[23redbull32]

I love you.

[Ahartwick38]

Thank you for your help!

[mathcat1]

very good explanation thank you

[Shaffer88falconfan]

good information nice for kids in high school

[musicadict100]

thanks a lot! I have to finish a project and I missed a day of school so when i came back today the teacher had no time to explain anything to me! i see what he meant now

[daddygreenjeens]

Good Vid. Thanks,

[frozenlicks]

halps alot....Ty

[homesdaf]

thank u i just started math agian and iam doing review right now this helped.

[KRASIMIRpro]

thank you helped me review for my exam

[shinj1reyes6]

excuse me sir. may i know if u r teaching engineering math. coz' that would help me a lot

[Lolly1524]

Thank you so much for the clear explanation! You are an awesome teacher.

[AlRichards314]

Thanks for the comment. I appreciate hearing from people that find my videos useful.

[Bakugantsuvai1]

@AlRichards314 I am stuck, how do I find the equation of the circle with x-intercepts 0 and 4 and y-intercepts 0 and 6?

[AlRichards314]

@Bakugantsuvai1 Draw a graph and plot these points and you'll find that the triangle that goes from (0,0) to (0,6) to (4,0) is a right triangle that is inscribed in the circle. That means that the hypotenuse that goes from (0,6) to (4,0) is a diameter of the circle. So the circle is the midpoint of the diameter [(0 + 4)/2, (6 + 0)/2] = (2,3). The radius is half the distance from (0,6) to (4,0) which is root(52). Hence the equation is (x - 2)^2 + (y - 3)^2 = 52.

[Bakugantsuvai1]

@AlRichards314 Thank you, I was stuck on the question for 2 hours already.

[Bakugantsuvai1]

@AlRichards314 is the radius supposed to be half of 52? the hypotenuse is root52

[AlRichards314]

@Bakugantsuvai1 Do you mean half root(25), not 52? The radius is root(25), so the diameter is 2Xroot(25).

[pauljonze]

Thank you so much. I'm trying to help my son with his school maths and I'm not familiar with this topic. Your video is far clearer and intuitive than his notes and I feel I have a complete grasp of the subject now. Please keep up the posts as they're invaluable!

[numbers326]

Life...Saver!!

i was on a trip and i have a test tomorrow on this and my teacher refuses to let me have a day to learn how to do it. This is a really amazing thanks a ton!

[back2themusic]

thank you friend

[morison68]

Thank You! This helps out alot.

[AlRichards314]

Thanks for the positive comment. I am very glad that my videos help some people understand and even enjoy math.

[sunshineolypops1394]

Just have to say i was so worried for grade 9 for math but i have been watching these and i am actually excited to start math.

THANKYOU so much for posting these it makes a huge difference.

i would have failed without these.

[Scooda912]

3:12 how is -3 squared 9 isnt it - 9 ??

[hoenoty]

-3 squared= -3 times -3

when you times to negative numbers together you get a positive

[virusdapimp]

yea dude, i agree with hoenoty

think of it like this

negatve times negative is always positive

positive times positive is always positive

negative times positive is always negative

positve times negative is always negative

[KX12508wins]

at 3:05 why does he put the negative three in brakets?? either way it makes 9

can anyone tell me

[mplestryrulesyoubich]

if it is -3 squared, then the 3 is squared first so it would mean -(32) so he puts it in brackets to make it -3 squared which is 9, not 3 square then negative making -9

[milkmanhoth]

very useful! wonderful teacher. thanks for teaching me, now i can confidently take my exit exam

[thabitpulak]

Very nice video sir! I especially liked the way you presented it on your computer in a clear, and interesting way.

If you don't mind, would you tell me what software you used for capturing your desktop movements?

[fuadorko]

hey! you watch these too?? lol

[thabitpulak]

Yeah...it helps with studies...

[fuadorko]

see....bengalis are smart.....we study on higher grades

[thabitpulak]

yah.....I guess so!

I am in 7th grade..what are you in?

[fuadorko]

8 but I have this book which i started in grade 7