# Mathematics: Post your doubts here!

Discussion in 'International A And AS Level' started by XPFMember, Sep 8, 2011.

1. ### Thought blocker

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Using Work Energy Principle,

1. Let the starting point be A and the end point be C.

2. List down Energies and Work at point A and C

Point A:
Ep = 0 J
Ek = 1/2 × 840 × 14^2 = 82320 J
Work done against resistive force = 0 J

Point B:
Height from the ground = 8sin30 - 10sin20 = 0.58m
Ep = 840 × 10 × 0.58 = 4872 J
Ek = 1/2 × 840 × v^2
Work done against resistive force = from part i we got it as 11520 J

3. Use the work - energy equation and solve for v

Point A = Point B

82320 = 4872 + 420v^2 + 11520

Thus, v = 12.5 m/s (3sf)

3. ### KashishV

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HI guys, so I wrote my AS level pure math 1 paper today and it was easy but I couldn't get a 6 marks question right :'((
they gave: y= [(x^3+x^2)]^0.5
and in the question, the very first thing we had to do was differentiate it. Now I'm usually good at differentiation. I can do the product rule, quotient rule and chain rule even. However I had this assumption, god knows why that in AS level at least, we can only apply the chain rule for linear equations. Then this question suddenly comes up and messes my whole grade up. I've searched and people use substitution method which is A level. Have you guys learnt this level of differentiation in your AS level too? or was it just me who didn't know?

4. ### Kanekii

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Sorry to hear that but you can differentiate it directly
Dy/dx=3x^3/[x^3+x^2]^0.5
We use quotient rule when we divide two different functions e.g x/x^2
We use product rule when we multiply two different functions e.g 3x.Cosx
We use chain rule when we three variables e.g x, y, t
Dy/Dx=Dy/Dt x Dt/dx.
Btw in differentiation we can differentiate linear or non linear equations.

Last edited: Feb 18, 2019
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5. ### KashishV

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Yes, I rechecked with my teacher too. The real fact was that you can only apply the chain rule to a linear equation while integrating. Stupid, stupid mistake.

6. ### Thought blocker

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This could be done with chain rule

7. ### KashishV

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I know now

8. ### sukasukinya

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Can someone help me with statistics 2? I do not know how to do question (ii). The answer is 0.865 :'(

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9. ### Emmris

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10. ### Ebrahim12

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(a)
Number of terms in the brackets = {1,2,3,...}
Number of terms in the first n brackets = sum of terms up to the nth bracket = sum of numbers from 1 up to n
So you use [n(n+1)]/2 to get that sum

(b)
Only the terms = {1,4,7,10,...}
It's a arithmetic progression with this formula:
t = 1+ (p-1)3
Were p is the position of the term t
The last term in the nth bracket will have overall position p = number of terms up to the nth bracket
We already have this from (a)

p = [n(n+1)]/2

Substitute p:
t = 1+ ( ([n(n+1)]/2) -1)3

Simplify:
t = (3n^2+3n-4)/2

(c)
We already have the formula for the last term in the nth bracket from (b)
(3n^2+3n-4)/2 > 628

solve for n:
3n^2+3n-1260 > 0
(n-20)(n+21) > 0
n > 20 or n <-21

Therefore, least value of n = 21

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11. ### Emmris

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Thank you

12. ### Khitan

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in a group of 30 teenagers 13 of the 18 males what kops are kid and 3 of the 12 female watch kops are kids find probability that the person chosen at random from the group is either female or watches kops are kids or both.
Nov 11 p63 q2
I need detail solution please .

13. ### Ebrahim12

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Please copy paste the actual question next time.

Q:In a group of 30 teenagers, 13 of the 18 males watch ‘Kops are Kids’ on television and 3 of the 12 females watch ‘Kops are Kids’.
(i) Find the probability that a person chosen at random from the group is either female or watches ‘Kops are Kids’ or both.

Ans:
The group can be divided into four:
13 - M watch
5 - M don't watch
3 - F watch
9 - F don't watch

P(F or watch or both) = N(F or watch or both)/N(total)
= (3 + 9 + 13)/30
= 0.833

You can also look at it as:
P(F or watch or both) = 1 - P( NOT [F or watch or both])
NOT [F or watch or both] == [M don't watch]
= 1 -P(M don't watch)
= 1 - 5/30
=0.833

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14. ### Khitan

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Is the method same for this question also?Why is there men not mentioned? But still we use men in counting

15. ### Ebrahim12

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Not sure what you mean by men not being mentioned. But it's a similar idea.

M H
M notH
F H
F notH

p(F or H or F H) = 1 - p(M notH)
Since M notH is the only group that won't be counted in (F or H or F H).
= 1 -(3/4)(2/5)

16. ### Mushraf altaf

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can someone solve this, i am not getting the answer right! thamk you

17. ### Zunaira Maniar

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You're right for the shading part. When you shade below the line for arg z <_ -pi/4 , then 2+rt2 makes sense

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18. ### Shemyaa

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STATS (Can someone help?)
The random variable X has the distribution B (20,p)
Given that p=0.7 and P(X≥x) >0.1, find the greatest possible value of x.
Is there a straight forward method rather than the long method of trying?

The answer is 17 just in case.
Thanks

19. ### Kanekii

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Need help with this

20. ### noor sajid

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Can someone plz help me with this.

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