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Sunday, February 04, 2007

Dixième Mathématiques KCVI

Si vous avez des questions vouz pouvez les demander ici.

10 comments:

Anonymous
said...

hi ms. Bearse, I didn't really understand question 5 on the chapter 2 test we got last week. (The last question talking about the 20$ canadian bills) it said that we had to factorise the expression, but then it also said that we had to sort of substitute the X for another number. So was there two parts to the question, did we have to factorise and then substitute or did we have to do something else?

Also, I'm having some troubles figuring out which factorisation method to use. I understand when to use the second method, but I'm not too sure in which case I use the first or the third.

Hi, question 5 was about finding the dimensions of the bill given the expression for its area. We need to use factorization to find out expressions for the two dimensions of the bill. The final part was to substitute a value of x into each dimension, and determine the value. 10x^2+9x-40 was the expression for the area of the bill. To factor the expression we find two numbers that have a sum of 9, and that have a product of -400. The two numbers are 25 and -16.

Now we replace 9x by 25x-16x 10x^2+25x-16x-40 then we take out a common factor from the first 2 terms, and also from the second 2 terms. 5x(2x+5)-8(2x-5) (5x-8)(2x+5)

So we know that the dimensions are (5x-8) and also (2x+5)

if x was 32mm, we can find that the dimensions are 5(32)-8=152mm, and 2(32)+5=69mm

As far as when to use what kind of factoring.... 1. always try to do common factoring first. 2. if you have a binomial, check to see if it is a difference of squares (2 square numbers with a - sign between them). Then you can factor it into a sum and a difference of the two roots of the square numbers. 3. if you are given a trinomial there is really only one way that you need to remember. ax^2+bx+c find 2 numbers that add up to "b" and that multiply to make the product of "a"x"c". NOTE: sometimes "a" is 1. factor the questions as I showed you up above.

I wouldn't really know how to do that question either...I'm confused by how many equals there are.

Let me take a guess at what you are doing.

solve by factoring when y=-36 y=x^2+12x at this point you'd substitute the -36 for y. -36=x^2+12x 0=x^2+12x+36 0=(x+6)(x+6) x+6=0 or x+6=0 (you don't need to write it twice though because both roots "racines" are the same) x=-6

Hello, it's Catherine from knitters. I finished my sock till the ankle liek you said and I need the pattern to make the heel. I must say my sock is really impressive. I also need the pattern to start the other sock.

can i meet you sometime tomorrow before the exam, i have a couple questions a bout completing the square, and some trig stuff, i will be at skool at the normal time

Hi Harrison, I was at choir practice this evening, sorry this response is late. I will be at school at 10:00 tomorrow morning. You can find me in the math office, or in room 207/203. I'd be happy to help you with your questions. I'm glad you're working so hard. See you at 10

Those questions weren't for homework...rather they were for those who had finished the test early, to give them something to do. We'll have a look at that page again tomorrow.

## 10 comments:

hi ms. Bearse,

I didn't really understand question 5 on the chapter 2 test we got last week. (The last question talking about the 20$ canadian bills) it said that we had to factorise the expression, but then it also said that we had to sort of substitute the X for another number. So was there two parts to the question, did we have to factorise and then substitute or did we have to do something else?

Also, I'm having some troubles figuring out which factorisation method to use. I understand when to use the second method, but I'm not too sure in which case I use the first or the third.

Thanks!!

Hi,

question 5 was about finding the dimensions of the bill given the expression for its area. We need to use factorization to find out expressions for the two dimensions of the bill. The final part was to substitute a value of x into each dimension, and determine the value.

10x^2+9x-40 was the expression for the area of the bill. To factor the expression we find two numbers that have a sum of 9, and that have a product of -400. The two numbers are 25 and -16.

Now we replace 9x by 25x-16x

10x^2+25x-16x-40

then we take out a common factor from the first 2 terms, and also from the second 2 terms.

5x(2x+5)-8(2x-5)

(5x-8)(2x+5)

So we know that the dimensions are (5x-8) and also (2x+5)

if x was 32mm, we can find that the dimensions are 5(32)-8=152mm, and 2(32)+5=69mm

As far as when to use what kind of factoring....

1. always try to do common factoring first.

2. if you have a binomial, check to see if it is a difference of squares (2 square numbers with a - sign between them). Then you can factor it into a sum and a difference of the two roots of the square numbers.

3. if you are given a trinomial there is really only one way that you need to remember. ax^2+bx+c

find 2 numbers that add up to "b" and that multiply to make the product of "a"x"c". NOTE: sometimes "a" is 1.

factor the questions as I showed you up above.

I hope this helps you. Have a good night!

just a quick question about factorising.

if y=4 and we have to factorise something like y=5x62 = 3x how do we do it?

i dont quite understand how to do it?

I wouldn't really know how to do that question either...I'm confused by how many equals there are.

Let me take a guess at what you are doing.

solve by factoring when y=-36

y=x^2+12x

at this point you'd substitute the -36 for y.

-36=x^2+12x

0=x^2+12x+36

0=(x+6)(x+6)

x+6=0 or x+6=0 (you don't need to write it twice though because both roots "racines" are the same)

x=-6

Sorry I didn't answer sooner. I hope this helps.

Ms. Bearse

Hello, it's Catherine from knitters. I finished my sock till the ankle liek you said and I need the pattern to make the heel. I must say my sock is really impressive.

I also need the pattern to start the other sock.

Many thanks.

I was just thinking of you...I'm adding a knitter's thing to this blog, and also to my website :)

I'll get a link to that pattern in a few minutes.

Congrats on knitting that so fast! I'm impressed.

can i meet you sometime tomorrow before the exam, i have a couple questions a bout completing the square, and some trig stuff, i will be at skool at the normal time

rsvp asap

thanks, harrison

Hi Harrison, I was at choir practice this evening, sorry this response is late. I will be at school at 10:00 tomorrow morning. You can find me in the math office, or in room 207/203. I'd be happy to help you with your questions. I'm glad you're working so hard. See you at 10

Hey Ms. Bearse

i forgot to copy down the homework after the test on friday could you please tell me the page number and questions and stuff thanks!

Those questions weren't for homework...rather they were for those who had finished the test early, to give them something to do. We'll have a look at that page again tomorrow.

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