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IGCSE MATHS Doubts

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Vin:

--- Quote from: Baladya on May 15, 2010, 01:00:27 pm ---Ya but how did you know it was y=0?

--- End quote ---

same way like u found 4 b) i)

mdwael:
Can anyone explain me how to do question 7 the C part page 15 in paper 4 maths year oct/nov 2009
I tried and I couldnt figure out anything the MS answer says its 27W and 4W  ???

Baladya:
for (i) u already have the lenght from a)i) this is the cirumference. Use C=pie(r^2) to find it.
(ii) Now u have the radius. Imagine the line h(height of cone). It makes a right angle triangle with the radius and AO. Use Pathegeroth rule to find the height.
 

Ghost Of Highbury:
ci ) 1/3 * pi * (3x)^2 * 3y = 9x^2y*pi

      W = 1/3 * x^2 * y * pi = (x^2ypi)/3

W * 27 = 9x^2ypi

27W

cii) 1/3 * pi * (2x)^2 * y = (4x^2ypi)/3

W = 1/3 * x^2 * y * pi = (x^2ypi)/3

W * 4 = (4x^2ypi)/3

4W

mdwael:

--- Quote from: A@di on May 15, 2010, 02:43:29 pm ---ci ) 1/3 * pi * (3x)^2 * 3y = 9x^2y*pi

      W = 1/3 * x^2 * y * pi = (x^2ypi)/3

W * 27 = 9x^2ypi

27W

cii) 1/3 * pi * (2x)^2 * y = (4x^2ypi)/3

W = 1/3 * x^2 * y * pi = (x^2ypi)/3

W * 4 = (4x^2ypi)/3

4W

--- End quote ---

I didnt understand  ??? can you make it simpler please? :-\

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