Answers (2 Viewers)

[k4t5UM0t0]

Post up answers to the relevant question and if possible show working

 

[fishy89sg]

is the answer to 8 (c) (iii) 2?

 

[JasonNg1025]

If it's the limit one, I punched it in my calculator and got 3.1415926535.. so I put in pi..

Can people also please post their answers to guessing the velocity of the raindrop hitting the ground? And also.. how did you do it

I just randomly put 6m/s

 

[fishy89sg]

If it's the limit one, I punched it in my calculator and got 3.1415926535.. so I put in pi..

Can people also please post their answers to guessing the velocity of the raindrop hitting the ground? And also.. how did you do it

I just randomly put 6m/s

omg how can i forget to put a number like n=1000 into the equation

 

[gaoOO]

hm, vladimirv and I both got pi^2/2

sin pi/2n -> pi/2n

 

[fishy89sg]

hm, vladimirv and I both got pi^2/2

sin pi/2n -> pi/2n

hey hey youre probably right lol
im just an average 4unit student lol

 

[AMorris]

raindrops question is 7 (u take the terminal velocity)

the last part of the last question is pi^2/2 (but I somehow forgot to square it and multiply by 2 so I only got pi/2)

 

[Hikari Clover]

回复: Re: Answers

man,it cant be pi.....

did u forget to put square ?

i got pi^2/2....

 

[jayel89]

does any1 remember the answers to the two probability questions???

 

[pires_w]

i put 0, since n goes to infinite, the "polygon" becomes a dot, or a circle, there fore p = 0, so p//q =0

 

[Golbez]

Re: 回复: Re: Answers

For the rain drop, using

v^2 = 49 (1 - e^[-2x/5])

as x -> infinity

e^[-2x/5] -> 0

So v^2 -> 49

v -> 7

EDIT: I also got 0 for the last question.

Because -

As n -> Infinity

sin(pi/2n) -> 0

therefore 2(nsin(pi/2n)^2 -> 0

Think about it logically... Why would a infinitely sided polygon be restricted to perimeter of pi/2 or something like that?

 

[pires_w]

Re: 回复: Re: Answers

For the rain drop, using

v^2 = 49 (1 - e^[-2x/5])

as x -> infinity

e^[-2x/5] -> 0

So v^2 -> 49

v -> 7

EDIT: I also got 0 for the last question.

Because -

As n -> Infinity

sin(pi/2n) -> 0

therefore 2(nsin(pi/2n)^2 -> 0

Think about it logically... Why would a infinitely sided polygon be restricted to perimeter of pi/2 or something like that?

lol, i did the rain drop thingy wrong, i thought the acceleration is 9.8, and obtain 0 for v XD

can anyone show me question 5di) please?
thz

 

[Golbez]

5di was kind of annoying...

Basically, BCP and BAP are similar coz they have equal sides/angles whatever.

And for a 4 sided polygon each interior angle is (n-2)180/5 degrees = 3pi/5

Therefore Angle BAP = 3pi/5 but bap and ead are pi/5 therefore angle cad = pi/5.

Also, Side AC = AP+PC

And cos (pi/5) = AP/1

So AP = u

Similarly, PC = u

And so AC = 2u

Similarly, AD = 2u


Using the cos rule,

CD^2 = AC^2 + AD^2 - 2(AC)(AD)Cos (CAD)

CD=1

1 = (2u)^2 + (2u)^2 - 2(2u)(2u)u
1= 8u^2 - 8u^3

Rearraging

8u^3-8u^2+1 = 0

As required.

 

[gaoOO]

Re: 回复: Re: Answers

For the rain drop, using

v^2 = 49 (1 - e^[-2x/5])

as x -> infinity

e^[-2x/5] -> 0

So v^2 -> 49

v -> 7

EDIT: I also got 0 for the last question.

Because -

As n -> Infinity

sin(pi/2n) -> 0

therefore 2(nsin(pi/2n)^2 -> 0

Think about it logically... Why would a infinitely sided polygon be restricted to perimeter of pi/2 or something like that?

well my solution is on the other thread, but logically p/q can't equal zero because p doesn't ever equal zero.





lim n--> infinity of 2 (sin pi/2n)^2

as n approaches infinity, pi/2n approaches zero. But lim x--> 0 of sin x = x

therefore it is equal to 2 (pi/2n)^2
= pi^2/2

 

[tanguyen]

Re: 回复: Re: Answers

Ah hah! Thanks for that Gao... couldn't think of the solution. I got zero as well and I asked the olympiad kid in my school and he said he got pi squared on two.

 

[Argen1447]

well along the lines of what gaoOO said,

if you think logically,

as n approaches infinity

n x sin(pi/2n) = really big number x really small number

so you're forgetting the 'really big number'

so you can't just assume it goes to zero

 

[Wellzy]

I've got a whole load of questions:

Q3. a) ii) Is the curve a refection in the y-axis for x<0

Q3. c) Anyone remember the area?

Q4. c) Something like "1/2 x (5e - e*2)"

Q6. b) iii) Physical significance of "-0.2v*2"

 

[fishy89sg]

I've got a whole load of questions:

Q3. a) ii) Is the curve a refection in the y-axis for x<0

Q3. c) Anyone remember the area?

Q4. c) Something like "1/2 x (5e - e*2)"

Q6. b) iii) Physical significance of "-0.2v*2"

3 a) yeh
c) 2 pi
4c yeh, but i had 1/2 + ...
6 b) lol i wrote something like "cause its proportional to the velocity" LOL

 

[blink376]

Hey what did people get for the perms and combs question

 

[Golbez]

6biv

-0.2v^2 is opposing gravity, so it would be air resistence.