Pure Maths 12 today........

[kevin24]

I am..

Any suggestion for essays title?

 

[kevin24]

I did.. Area = Area of rectangle - Area of all three triangles. i got it like that. what did you do?

Same.

 

[Nishii]

Y has u put the less sign the sum of all angle is equal to 360 degrees not less than! And the answer is 18.

Yes.. but i used the formula to find the last term. and the last term must be less than 360 degrees, right? How did you get 18?

 

[Nishii]

Any suggestion for essays title?

No idea.. probably same as http://general-paper.com/probable-questions-for-mayjune-2012

 

[kevin24]

Yes.. but i used the formula to find the last term. and the last term must be less than 360 degrees, right? How did you get 18?

But all the term are less than 360 degrees! I have used sum of AP Sn=n/2{2a +(n-1)d} subst values of a and d and equate it to 360 degrees. Maybe a was 3.

 

[Nishii]

But all the term are less than 360 degrees! I have used sum of AP Sn=n/2{2a +(n-1)d} subst values of a and d and equate it to 360 degrees. Maybe a was 3.

Yeah a was 3 and d was 2 i think.. you managed to work out the quadratic equation?! .. dont know which one is correct..!

 

[Nishii]

But all the term are less than 360 degrees! I have used sum of AP Sn=n/2{2a +(n-1)d} subst values of a and d and equate it to 360 degrees. Maybe a was 3.

and when you do it one by one, i mean 3+2+2+2+..... it take 179 times to reach 360 degrees! (i checked it at home!)

 

[kevin24]

No idea.. probably same as http://general-paper.com/probable-questions-for-mayjune-2012

I'm sure there will be essays on recession and election in US.Don't u think so.....

 

[Nishii]

So I think its another mistake I have done. I only calculate the second derivative and answer that the minimum is 0.

Me too! how many marks do i lose if i did only the second derivative and find the minimum value?

 

[kevin24]

Yeah a was 3 and d was 2 i think.. you managed to work out the quadratic equation?! .. dont know which one is correct..!

I got a quadratic eqn like that n2 -n+360 =0 And factorising it (n-18)(n+20)=0 Where n=18.

 

[kevin24]

and when you do it one by one, i mean 3+2+2+2+..... it take 179 times to reach 360 degrees! (i checked it at home!)

When you doing this you are assuming that the circle is divided into n equal parts which is not so as the question said that the two smallest degrees are 3 and 5.

 

[kevin24]

Me too! how many marks do i lose if i did only the second derivative and find the minimum value?

Maybe 1 or 2.

 

[Nishii]

When you doing this you are assuming that the circle is divided into n equal parts which is not so as the question said that the two smallest degrees are 3 and 5.

yeah, you convinced me. i got it wrong But when you Subst a=3 d=2 and n=18 in formula of Sn, you get 333. why??

 

[kevin24]

yeah, you convinced me. i got it wrong But when you Subst a=3 d=2 and n=18 in formula of Sn, you get 333. why??

I think u are mistaken s18=18/2{(2*3)+(18-1)(2)}=360.

 

[rizwaan]

I got 18
a=3
d=2
sum= n/2 X (first + last)
360 = n/2 X (3+3+d(n-1))
720 = n(6+2(n-1))
720=6n+2n^2-2n
720= 4n + 2n^2
360=2n + n^2
(n-18)(n+20)=0
n=18

I got a=3 and d=2 and used the wrong formula. how many marks will i get?

 

[Nishii]

I think u are mistaken s18=18/2{(2*3)+(18-1)(2)}=360.

Yeah! thanks

 

[rizwaan]

I did l=a+(n-1)d < 360 degrees and got 179! :s

I also did the same thing and got 180. how many marks will we lose because the value of a and are correct. we have just used the wrong formula.

 

[Nishii]

I also did the same thing and got 180. how many marks will we lose because the value of a and are correct. we have just used the wrong formula.

All of it i think it was 3 points, right? probably one point will be for using the right formula, 2nd point for getting a quadratic equation and 3rd for getting the correct value

 

[Z.S.M]

The question was about the minimum value of the 'Gradient' not the curve,So DY/DX of the curve is the equation of the tangent,D^2Y/DX^2 is the second deff of curve but first deff of Gradient,so you get D^2Y/DX^2 and equal it to 0,get the X substitute it into DX/DY to get minimum value of 'Gradient',and to make sure that it's a minimum value I got Third deff which was second deff of gradient got a positive product which means it's minimum.

Yeah..... i thought it out on the same lines! and what minimum value did you get?

 

[Z.S.M]

No it was much easier ... Fist 9 questions were very easy

Yeah........ Q 10 and 11 REALLY had me going though......