evaluate 3x3 determinant

[n0vabahamut]

thank you so much i love you!

[adadaddddaaa]

There is a lot simpler way to do 3x3. In this case you just do 3x7x-4 + 3x1x-1 + 3x7x5 - (-1)x7x3 - 5x7x3 - (-4)x7x3. Thats adding products from top left to bottom right all 3 diagonals and then subtracting from bottom left to top right all 3 diagonals

[tarek12mig]

lol....i just got that thing when i was in (class 5) x)

[engmaisoon]

its not working for all cases !

thx anyway :)

[datboiy20]

thanks.

[SorrowHarvester42]

The way they teach us here is so much less efficient

[jhiggzaw]

I just love Math, when you spend 3:37 watching other people solve, and then they have a 0 for an answer at the end! LOL!

Thanks so much for the vid! Missed my class last week so I have to learn it "the easy way" through YouTube to survive our Final Exams tomorrow.

Thumbs up for you.

[stratoge]

My teacher doesn't even go by the book (which is the method ur doing). He uses his own special method which probably half of the class probably is confused about.

[65eshine]

You explained this so clearly and easy to follow! Thank you so much, you just don't know how helpful your videos are to myself and many other viewers, despite the few rabble rousers!

[triplemango101]

THANK YOU SOOOOOOOOOOOOOOOO MUCH!

I spent around 3 hours trying to figure out how to do these types of problems. You made it SO easy for me to understand. Please, continue to post videos on Algebra 2/Trig. because you are AMAZING at explaining.

Thank you once again for this!

[Belmoth1]

my textbooks explains it but it is somehow the opposite of what you say, WHICH ONE WILL A BELIEVE?!?

[robichaudd]

@Belmoth1 Your book probably expands around the first row instead of the first column. See my replies to poontang3zizo for more details. Either method will give the same answer. But check with your teacher to see if there's a preferred method.

[tygamann1]

did you just erase marker with a pencil eraser?

[The3rdNipple]

it's too confusing... lmfao

[poontang3zizo]

the coefficients of each of the 2 x 2 matrices are NOT 3, 7 and 1. It should be 3,3,3. The TOP COLUMN should have your values. This is VERY VERY VERY WRONG. Please remove this vid before it really messes up someone who is trying to learn

[robichaudd]

@poontang3zizo You can expand around any row or column, providing you use the following sign pattern for the terms in the expansion:

+ - +

- + -

+ - +

Because I expanded down column 1, I used the sign pattern + - +; if I had expanded across row 2, I would use - + - ; etc.

[poontang3zizo]

@robichaudd

That may be true, you will get the same solution, however it is a bad convention to follow.

I say this because when doing the cross product of lets say a unit vector this method might make it difficult to grasp. I say this because the i, j and k are on the columns and not the rows. I admit your method might not be 'wrong' but it sure will make the dot product confusing

[robichaudd]

@poontang3zizo Ahhh, yes, I see your point. Thanks for clarifying. I added another annotation with a link to a video of a vector cross product being done out (it's a khanacademy video - great channel with tons of math videos).

If I get more feedback about the method I show being confusing, I'll certainly delete the video and repost one with expansion across the top row.

[poontang3zizo]

@robichaudd

I meant to say 'cross product' and not 'dot' in the last line :P

And sure no problem. Thanks for taking the time to reply

Cheers

[juns1992]

Excuss me, you are going completely wrong direction here you should take first row as a coefficient not the column. This may screw a person's math test please delete this madness

[poontang3zizo]

@juns1992

Very good observation. This indeed is madness

[robichaudd]

@juns1992 I've added an annotation in the video showing the sign pattern to use for whatever row or column you expand on. Hopefully this will clear up any confusion.

[aa111r]

@robichaudd thanks for such a nice video

[Gmoral69]

OMG thank you , you explain this much better than my proffessor

[Kiwi663]

So you always subtract when you get the det.?

[robichaudd]

@Kiwi663 To evaluate the 2x2 determinants, always do "top left times bottom right" minus "bottom left times top right." Sometimes you'll get a double negative that turns the subtraction to addition, but always start with subtraction.

[Dabilahro73]

excellent video! thanks a bunch!

[anheroinEVERYDAY]

why do you say take away it makes me want to close the video

[cmw1clmt]

what about for dx1 dx2 dx3?

[donkyg182]

Thanks ! very useful

[robbiesoho]

well done. very clear

[austin123457]

I love you.

[Rgymnastwebgirl]

I am actually learning this in the 8th grade. I'm in Algebra 1B getting half a high school credit last year and the other half this year. Next year I'll be in geometry for the 9th grade.

[Rgymnastwebgirl]

What do you have to do to the numbers that are still in the matrix if the pattern is not -+-? do you just change it, or is it some long process?

[robichaudd]

@Rgymnastwebgirl Use the sign pattern as a starting point, then insert the matrix element as-is. For example, if the sign pattern is + - +, then you'd have +(element)(2x2 det) - (element)(2x2 det) + (element)(2x2 det).

[Thegthatkillsall]

what would happen if that -1 wasnt negative

[robichaudd]

@Thegthatkillsall For the last parentheses when working out the 2x2 determinants you'd have +1(21-21) instead of -1(21-21). But in both cases we're multiplying the +1 or -1 by 21-21=0. So the final answer for the 3x3 determinant will be same whether the a +1 or -1 is present.

[naveed03316477347]

ThanX

[Sakura7981]

Thank you thank you thank you you have no idea how much you have helped me

[lbethinked]

You are a lifesaver!!!! THANK YOU!

[dixseez]

..Thanks a lot Yo'

[DaiPodAppReviewer]

be my algebra 2 teacher plz ?

[ronan462]

Thank you! possibly just saved my life on this test today

[teddybearhugger5]

aaaaaaaaaaaaah thanks! I was so confuzed....:D

[bushlovessatan]

Thank you so much for your help! You rock!

[mrmichael20]

you are so helpful, Thank you very much !

[eliplink12]

thanks

[ssbkid]

Thank you so much for making this.

[klferdz]

How if it includes a variable example. 3t 7t -1t? :D

[SilentQ]

why do i get -168?

First row i got =-189

2nd row i got = -21

3rd row i got = 0

D= -168 ?

[robichaudd]

@SilentQ The second row should result in +189 because it's -7(-12-15). Looks like you did -7(-12+15) instead.

[SilentQ]

sdasda

[fricomarcelo]

Thanks, good video!

[Hammiepuu]

I'm in 10th grade and I'm taking this ffffffffffffffffffffffffffffff­ff

[jazmin1234521]

@Hammiepuu I'm in 9th grade and im doing this

[ninja8373]

Thanx a lot mam... u explained everything in a simple way which our tutors couldn't do..

[L4DL4D2EUROPE]

Very nice thanks

[3alazagg]

I LOVE YOU!!!!!!!!!!!!!!!!!

[nissimvas]

thanks

[EKAM3000]

determinants of square matrix is easy than that.....

[007dardan]

What grade level is this >>?? i.e high scholl or university thanks :)

[robichaudd]

@007dardan The course I made the video for is at a college. This material is taught in high school too.

[Hashimlokasher]

@robichaudd It is for College

[brashboy0403]

@007dardan

i'm in year 11 but doing it as a year 12 VCE subject...

so yeh, high school

[kate7047]

THANK YOU! This was amazingly helpful!

[DeadCanvas]

you should the viewers that the signs should be fixed like

+ - +

- + -

+ - +

[dbnfsdf1006]

I just want to understand why + - +

[tcraiford]

@dbnfsdf1006 Because it makes a funny face when you put it that way

[kukufied]

@dbnfsdf1006 one day the tooth fairy visit robichaudd and told her, " '+-+' !"

[sammysrh]

Wow AWESOME!! thank you!! Because of you i might pass algebra 2 now!! thank you!!!!! I didnt understand it because i do online school and its not very descriptive!!

[falconboy85]

it's totaly wrong ...

[WickedEsbjerg]

this is the wrong method .. you use the first horizontal line, not the vertical

[robichaudd]

Any row or column works - see my reply to epjman345...

[nubsan]

yesss

[Jontheking100]

@robichaudd Worked for me...

[paperfreeck]

@robichaudd Thats right try it ... in some books they use the horisontal first line and in some other books the vertical first column. Saurus method is better easier to remember for me, but it doesnt apply for 4x4 matrix.

[freeocean09]

thanks alot, u showed me an easier way

[SnuffyWuffles]

thanks so much for this...it's a shame that I spent a fortune on a textbook that can't explain how to solve this type of problem in a way that makes sense. At any rate, thanks again -- you made my night!

[xxhipblogger]

Why it zero? is it because it is the last answer or what?

[robichaudd]

If you completely do out the last line shown in the video you get:

=3(-63)-7(-27)

=-189+189

=0

[electricmaster23]

@robichaudd took me a while even after reading it a few times but i eventually understood so thanks ^^

[ymama35]

this is great :D

[sincha3]

great! :) thank you!

[hmodywakid]

this method is not good i asure u

[skoushik333]

Is there any faster method to do this? :(

[robichaudd]

Not really. But if there's a row or column that has alot of zeros in it, use that row or column to expand around. Be sure to use the correct sign pattern for the row or column you choose. See my reply to epjman345 for info on sign pattern.

[skoushik333]

Oh.. Now i get you.. I didn't know you could do that.. Thanks a lot :D

and btw, u use the same sign pattern for finding the Co-Factor Matrix too rite?

[robichaudd]

use the sign pattern anytime you evaluate a determinant larger than a 2x2

[skoushik333]

Ok Thanks a lot for the help :)

[NightmareXsk8r]

Is there a video about doing this by 2x2? Knowing the fact you have over 100 vids I can't find any. [Not the best at finding stuff]. If you don't can you make a video? If you do is there a link?

[robichaudd]

I don't have any videos on 2x2 determinants. If searching in youtube doesn't work try a google search, there should be plenty of results there.

Basic idea is, if top left is 2 and top right is 3 and bottom left is 8 and bottom right is 6, determinant is equal to top left times bottom right minus bottom left times top right: 2*6-8*3=12-24=-12. Always follow that pattern and you'll be all set.

[Alejo1691]

thanks so much

[tangointhesea]

THANK YOU!! got a math final coming up in an hour and my book never went over thses or the 2x2 and Im being tested on it anyways! thanks again

[epjman345]

I thought that you used a row rather than a column does it matter?

[robichaudd]

You can use any row or column, just watch the sign pattern. Make a 3x3 setup with the sign pattern of top row + - +, second row - + -, third row + - +. Whatever row or column you choose to expand from follow the sign pattern from that 3x3 sign setup for that particular row or column. Hard to explain in words...hope that made sense.

[epjman345]

Thanks a million! I just had a test over 4 chapters, and about half the questions incolved 3 by 3 matricies(???) and the test was about 33% of my grade. I probably would have failed if not for your help!

[hammervalve48]

thank u........

[sp00nEg6]

College professors like to make this seem harder than it actually is...

You made it so much more simple. Thank you.

[shadowzice]

Ty for the help (=

[cbarragan9]

this is the best method ive ever seen for this problem! THANK YOUUUUUUUU!!!!!!!

[me2005]

thank you so much!!! i have been sitting @ this for hours flipping through my book!

[jasonguyperson]

from now on resort to youtube first! (i do...)

^_^

[Ole199104]

This so much better than the version I learned at school. Thank you;)

[AjninEzakimak]

You're freaking awesome. This helped me so much.

[p3rf3c7]

thanks, thats great.

[beefyjerk]

wow, thank you! my math teacher is so lazy! our entire class didn't understand a lesson so she just skipped it and never bothered to re-explain it!

[tennisgirl813]

thank you so much! that made it so easy to understand!

[Nandine2]

yeah! your doing matrices now. good explanation