Qualification > Math
IGCSE MATHS Doubts
Ghost Of Highbury:
Radius = X
Height = y
Volume or W = 1/3 * x^2 * y * pi = (x^2ypi)/3
3 times --> Radius = 3x
Height = 3y
VOlume = 1/3 * pi * (3x)^2 * 3y = 9x^2y*pi
W = (x^2ypi)/3
Vol. = 9x^2y*pi
W * 27 = Vol.
27W
----------
cii) Radius = 2x
Height = y
Vol. = 1/3 * pi * (2x)^2 * y = (4x^2ypi)/3
W = (x^2ypi)/3
W * 4 = Vol.
Therefore, 4W
PS : Volume of a cone = 1/3*pi*r^2*h
mdwael:
--- Quote from: A@di on May 15, 2010, 03:01:13 pm ---Radius = X
Height = y
Volume or W = 1/3 * x^2 * y * pi = (x^2ypi)/3
3 times --> Radius = 3x
Height = 3y
VOlume = 1/3 * pi * (3x)^2 * 3y = 9x^2y*pi
W = (x^2ypi)/3
Vol. = 9x^2y*pi
W * 27 = Vol.
27W
----------
cii) Radius = 2x
Height = y
Vol. = 1/3 * pi * (2x)^2 * y = (4x^2ypi)/3
W = (x^2ypi)/3
W * 4 = Vol.
Therefore, 4W
PS : Volume of a cone = 1/3*pi*r^2*h
--- End quote ---
I think I got it now but why all this working and it only carries 1 mark so shouldnt there be a quicker way maybe like 3^3=27?
Ghost Of Highbury:
I had to show all the working for ur explanation. u just have to know wat to multiply to W to get the new volume.
ankitd_1994:
--- Quote from: ~VIN1094~ on May 07, 2010, 12:19:23 pm ---n also b) ii)
theres a great method my teacher taught me...
(y) x U = X
(a b) (-1 -4 -4 ) ( -1 -4 -4)
(c d) (1 1 3 ) = ( 2 5 7 )
multiply a b c d in matrix y to matrix U (they are the positions of the image, row 1 is x axis row 2 is y )
( (-a + b) (-4a+b) (-4a + 7b) )
( (-c+d ) (-4c +d) (-4c+ 7d) )
now solve any two equation my simultaneous method...
so, -a +b = -1 (because the position of this equation is corresponding to matrix "X", look for the colours)
-4a + b = -4
by solving u get a = 1 , b = 0
same for 'c' and 'd' ..u get d= 1 and c = -1
i dont expect u to understand but this method is really good n its really difficult for me to teach online..:(
read it n try to follow the steps while solving the paper u might get it...:) :)
--- End quote ---
ya got the method bt u dont need to use it for all 3 pts only 2 will do fine
mdwael:
in May/June paper 4 2009 page 19 d(ii) part (its the last question in the paper) how do you get 1711 and 1770 I got 58 and 59 can someone please explain?
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