queries 2004 (1 Viewer)

[totallybord]

hey,
can someone explain this from the 2004 paper?
4) c) how do you know that PQ is perpendicular to the x axis? is it some property of an ellipse that i shld know or something?
5)b)i) in how many wya can n students be placed in 2 distinct rooms so that neither room is empty?
and ii) in how many ways can 5 studnet be placed in 3 distinct rooms so that no room is empty?
i dont get the working out from jeff gehas thing or the logic
c)i) why is r/sin@ =R? how do you know??

many many thanks

 

[bazza159]

k well for the conics one, redraw the diagram for part ii. The tangents to the ellipse can only occur if P and Q are vertically above one another.

i found the probability part confusing ha.

and sin@ = r/R (R being the radius of the sphere and r being the radius of the hoizontal circle).

So Rsin@ = r

 

[independantz]

5
B) i- to arrange n students in 2 rooms without 1 being empty, i think that's the q ? from memory

you can arrange n students in 2 rooms 2^n ways, however in all these 2 of these cases the rooms are empty

therefore A= 2^n-2

C i, the Radius of the sphere is R, and the radius of the cross section is r, sin(theta)= r/R

 

[totallybord]

thank you guys
i dont get the probability stuff