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Author Topic: 3U Maths Question Thread  (Read 1230260 times)  Share 

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RuiAce

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Re: 3U Maths Question Thread
« Reply #660 on: September 09, 2016, 06:01:29 pm »
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(Image removed from quote.)

how to do part a  iii)
That question doesn't make sense to any of us. Mind telling us where you got it from?

katherine123

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Re: 3U Maths Question Thread
« Reply #661 on: September 13, 2016, 01:31:12 pm »
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In each game of chess that Bobby plays against Boris there is a probability of 1/3 that Bobby wins, a prob. of 1/6 that Boris wins, and prob. of 1/2 that the game is drawn. They play 4 games.
i) find prob. that Bobby wins 2 games and Boris wins 2 games
ii) find prob. that Bobby wins 1 game, Boris wins 1 game and the other 2 games are drawn.

answer:
i) 4C2(1/3)^2(1/6)^2
ii)4C2(1/2)^2(1/3)(1/6) *2

i get the answer for i) but i dont understand why there is a need to multiply 2 for part ii)



ques2 :
Consider x^2=4ay with focus S. The normal at P(2ap, ap^2) meets y axis at R and triangle SPR is equilateral
i) normal at P is x+py=2ap+ap^3
ii) R(0, a(2+p^2)
iii) prove SP is equal in length to latus rectum, that is 4a units

not sure how to do part iii)
« Last Edit: September 13, 2016, 01:34:39 pm by katherine123 »

jamonwindeyer

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Re: 3U Maths Question Thread
« Reply #662 on: September 13, 2016, 02:27:21 pm »
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In each game of chess that Bobby plays against Boris there is a probability of 1/3 that Bobby wins, a prob. of 1/6 that Boris wins, and prob. of 1/2 that the game is drawn. They play 4 games.
i) find prob. that Bobby wins 2 games and Boris wins 2 games
ii) find prob. that Bobby wins 1 game, Boris wins 1 game and the other 2 games are drawn.

answer:
i) 4C2(1/3)^2(1/6)^2
ii)4C2(1/2)^2(1/3)(1/6) *2

i get the answer for i) but i dont understand why there is a need to multiply 2 for part ii)

Hey! So the answer without that extra multiplication accounts for selecting which games are drawn/won, then the probability of these occurring. We multiply by two to account for the fact that the two games won by Boris and Bobby can be swapped, as in, once we've chosen which games they'll win, there are then two different allocations to those games :)

ques2 :
Consider x^2=4ay with focus S. The normal at P(2ap, ap^2) meets y axis at R and triangle SPR is equilateral
i) normal at P is x+py=2ap+ap^3
ii) R(0, a(2+p^2)
iii) prove SP is equal in length to latus rectum, that is 4a units

not sure how to do part iii)

For Part (iii), we need to use the fact that the triangle SPR is equilateral, meaning SP=PR=RS. So, if we can prove any of those sides is equal to 4a units, our job is done. Let's just get expressions for all three (if you spot what to do straight away, that's awesome too):



All of these must be equal by definition, therefore we can say that:



Then we go back and pop that in our distance equation for SP:



Hope this helps! ;D

Ali_Abbas

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Re: 3U Maths Question Thread
« Reply #663 on: September 13, 2016, 09:13:40 pm »
+1
ques2 :
Consider x^2=4ay with focus S. The normal at P(2ap, ap^2) meets y axis at R and triangle SPR is equilateral
i) normal at P is x+py=2ap+ap^3
ii) R(0, a(2+p^2)
iii) prove SP is equal in length to latus rectum, that is 4a units

not sure how to do part iii)



« Last Edit: September 13, 2016, 09:21:30 pm by Ali_Abbas »

lha

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Re: 3U Maths Question Thread
« Reply #664 on: September 17, 2016, 08:14:27 pm »
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Can anyone give me a rundown on parametrics or tell me where i can find something that will explain it easily?

conic curve

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Re: 3U Maths Question Thread
« Reply #665 on: September 17, 2016, 08:15:44 pm »
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Can anyone give me a rundown on parametrics or tell me where i can find something that will explain it easily?

Watch eddie woo videos on Youtube

RuiAce

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Re: 3U Maths Question Thread
« Reply #666 on: September 17, 2016, 08:30:28 pm »
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Can anyone give me a rundown on parametrics or tell me where i can find something that will explain it easily?
Look for where it says parametrics

lha

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3U Maths Question Thread
« Reply #667 on: September 19, 2016, 06:52:06 pm »
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What should you do in the 5 mins reading time?


Look for where it says parametrics
Watch eddie woo videos on Youtube

Thank you!!!

Edit: Posts merged, avoid double posting, use the Modify and Insert Quote functions instead!
« Last Edit: September 19, 2016, 06:58:56 pm by jamonwindeyer »

jakesilove

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Re: 3U Maths Question Thread
« Reply #668 on: September 19, 2016, 07:04:07 pm »
+1
What should you do in the 5 mins reading time?


Thank you!!!

Edit: Posts merged, avoid double posting, use the Modify and Insert Quote functions instead!

In the five minutes, I usually try to answer as many multiple choice as I can after I quickly flick through the paper. In Ext 1, you're not going to really get far on any major question, so I think multis is the best way to go!
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RuiAce

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Re: 3U Maths Question Thread
« Reply #669 on: September 19, 2016, 08:06:21 pm »
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What should you do in the 5 mins reading time?


Thank you!!!

Edit: Posts merged, avoid double posting, use the Modify and Insert Quote functions instead!
In the five minutes, I usually try to answer as many multiple choice as I can after I quickly flick through the paper. In Ext 1, you're not going to really get far on any major question, so I think multis is the best way to go!
On the other hand (but still overlapping) I only do about 1-3 multiple choice questions. I take enough time to look at the paper and actually know what's going on. I look out for questions that will throw me off and brace myself for those.

jamonwindeyer

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Re: 3U Maths Question Thread
« Reply #670 on: September 19, 2016, 08:10:51 pm »
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On the other hand (but still overlapping) I only do about 1-3 multiple choice questions. I take enough time to look at the paper and actually know what's going on. I look out for questions that will throw me off and brace myself for those.

To throw in my 2 cents as well, I'd probably be more similar to Rui. The first thing I do is look through the paper, try and spot any doozy questions, get my brain chugging on them in the background. That could take all of the reading time and that was okay with me ;D if I did have leftover reading time, I did the MC ;D

jakesilove

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Re: 3U Maths Question Thread
« Reply #671 on: September 19, 2016, 08:12:57 pm »
+1
On the other hand (but still overlapping) I only do about 1-3 multiple choice questions. I take enough time to look at the paper and actually know what's going on. I look out for questions that will throw me off and brace myself for those.

And finally, 5 minutes is enough time to say 'I think I can' about 150 times. At the end of the day, no matter what you do in the 5 minutes reading time, the important thing is to be in the right mindset. If finding tricky questions, and feeling safe in knowing you can figure out how to do them, is the way to make you feel comfortable, go for that. If reading the formula sheet, or listing pneumonic devices, is your thing; do that. Reading time isn't a huge factor in exam success (although, if you use it in a way best suited to you, it can be very effective)
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massive

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Re: 3U Maths Question Thread
« Reply #672 on: September 23, 2016, 01:47:41 am »
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Hey guys how do you do part ii and iii for the q attached??

RuiAce

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Re: 3U Maths Question Thread
« Reply #673 on: September 23, 2016, 09:25:14 am »
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Hey guys how do you do part ii and iii for the q attached??
Part (iii) is easy. Clearly r=6 and n=12 so just sub it into the formula for (ii).
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« Last Edit: September 23, 2016, 09:35:19 am by RuiAce »

Neutron

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Re: 3U Maths Question Thread
« Reply #674 on: September 23, 2016, 01:49:59 pm »
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Hi! This is a silly question but I never understood how to do these types of polynomials :/

P(x)=(x+1)(x-3)Q(x)+(-2x+6)
Where Q(x) is a polynomial.
Find the remainder when P(x) is divided by (x+1)(x-3)

Sorry if this is dumb D: Thank you!

Neutron