IGCSE starting on Friday... pls.post doubts, important notes etc.

[Min Thaw]

no ..that's from GCE Core Mathematics C1 Advanced Subsidiary Mock Paper ^^

 

[Stancy Motha]

Sorry but we never did that...and wat we never did we ppl never know...tis the truth...

 

[Khin Lamin Thaw]

Sorry but we never did that...and wat we never did we ppl never know...tis the truth...

Absolutely TRUE..
@Min Thaw :

 

[Stancy Motha]

A solid wooden right circular cone has a slant height of 15cm and a total surface area of 54pi cm^2
a)Show that the radius of the base of the cone is given by
r^(2) +15r-54=0
b)Calculate the perpendicular height, in cm to 3sgf, of the cone.

 

[Min Thaw]

pi r^2 + pi*r*l = 54 pi
divide the whole equation with pi
r^2 + 15r = 54
r^2 + 15r -54 =0

perpendicular height = 14.7

 

[Khin Lamin Thaw]

a. (pi)r^2 + (pi)rl = 54pi ( total surface area = curved surface area + base area
(pi)r^2 + 15(pi)r = 54pi
(pi)(r^2 + 15r ) = 54 pi ( factorize "pi" )
r^2 +15r = 54 ( "pi" cancels )
r^2 + 15r -54 = 0 {shown}

b. r^2 + 15r - 54 = 0
( r-3 )(r+18 ) = 0 ( factorizing the quadratic equation )
r = 3 or r = -18(reject; it is negative )

let perpendicular height be "h"
h^2 = 15^2 - r^2 ( pythagoras' theorem )
h = square root of 225 - 3^2
h = square root of 216
h = 14.7 cm ( 3.sig fig)

 

[Min Thaw]

differentiate [x^3+2(x^2)+5x]^3

 

[Khin Lamin Thaw]

Use chain rule:

Let g(x) = x^3

Let h(x) = x^4+3x^2 + 5x

By chain rule we get:
g'(h(x)) * h'(x)

3(x^4+3x^2 + 5x)^2 (4x^3+6x+5)

Its up to you whether or not you want to try for like terms and simplify

P.S. i dun understand it either but i copied it from answers. yahoo... ~bla~bla

 

[Stancy Motha]

ok i no this is wrong but anyways
(9x^2+12x+15)^2

 

[Min Thaw]

okay then..here's my solution => let m = "x^3+2(x^2)+5x"
let y = "[x^3+2(x^2)+5x]^3
y= m^3
dy/dm = 3m^2

dm/dx = "3x^2 + 4x +5

dy/dx = "dy/dm * dm/dx
dy/dx = 3[x^3 + 2x^3 +5x ]^2 * 3x^2 +4x +5

 

[Stancy Motha]

Given that G=a/b
find the percentage decrease in the value of G when a decreases by10% and b increases by 20%

 

[Min Thaw]

25%

 

[Stancy Motha]

yup


The volume of a solid varies directly as the cube of the length of its longest side.
When the length of the longest side is
d cm, the volume is V cm3
.
When the length of the longest side is
D cm, the volume is 3V cm3
.
Find an expression for
D in terms of d
.

 

[Min Thaw]

pls solve this ...no .6

 

[Min Thaw]

D= [2Vd^3]^(1/3)

 

[Stancy Motha]

d* cube root 3

 

[Min Thaw]

d* cube root 3

great!

 

[Stancy Motha]

ok Q6. draw two lines parallel to AB so one will be on top and one on the bottom and one at the side using a compass set to 2cm..At point A now draw a semcircle which will join the top and bottom parallel line do the same at point B.

 

[Min Thaw]

what about the points between A and B?

 

[Stancy Motha]

Draw the complete locus of points in the plane which are 2 cm from the line AB