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Mathematics: Post your doubts here!

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0ct-nov 08
7i) first you have to find the perimeter of both the square and circle then add both and equate to 80cm.( because 80cm is the total length)
so,
Perimeter for square = 4x , for circle = 2(pi)r hence,
4x + 2pi*r = 80 divide everything by 2 and make r subject of formula
==> r = (40 -2x)/pi
now find area, area of square = x^2 , area of circle = pi*r^2
so, A = x^2 + pi*r^2, if u substitute r into this equation u will find ur answer

10 (iii) here u use the completion of square method:
h(x) = 6x - x^2
= -(x^2 - 6x)
= -[x^2 - 6x + (-3)^2 - (-3)^2]
= -[(x - 3)^2 -9]
= 9 - (x - 3)^2

(iv) here u have to find inverse of h:
h(x) = 9 - (x-3)^2
let y = 9- (x-3)^2
(x-3)^2 = 9 -y, taking square root both sides
x - 3 = +/ - sq.root of(9-y)
x= 3 +/- sq.root of(9-y) hence
inverse of h = 3 +/- sq.root(9 -x)
hope u got it :)
Thanx.. i got Q7(i), but cud u plz xplain how exactly u used the completing the squares method in 10(iii)..n 10(iv) the ans in ms is 3+root(9-x), theres no minus
 
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0ct/nov 07
m not so sure of q4

9i) here since they are asking u to find equation of the curve u have to integrate dy/dx
if u integrate dy/dx u'll get:
y= 4x - (x^2 / 2) + c
u have a point (2,9), substitute this point and find the value of c:
===> 9 = 4(2) - (2^2 / 2) + c
c = 3
then substitute c in ur equation and u'll have ur answer :
y = 4x - (x^2 / 2) + 3

ii) here u will have to find the gradient of normal first then u can find the equation, to find grad. of normal first find grad of tangent (i.e dy/dx) at x=2
so,
dy/dx at x=2 will be = 2
now to find grad of norm use m1*m2 = -1
u can let m1= 2 (grad of tangent) so ur m2 = -1/2
now since u have the gradient of normal and a point (2,9) u can find the equation using:
y - y1 = m(x -x1) and u'll get
y = 10 - x/2
hope u understood :)
oh so q9(i) is on intergration?...i havent yet learnt intergration..sry 4 the trouble:oops:..n sry it was supposed 2 be q9(iii), not q9(ii)..so if u cud plz ans dat:D
 
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oh so q9(i) is on intergration?...i havent yet learnt intergration..sry 4 the trouble:oops:..n sry it was supposed 2 be q9(iii), not q9(ii)..so if u cud plz ans dat:D
ok to find co-ordinates of Q u have to solve the equation of the curve and the equation of the normal simultaneously. if u do that one of ur co-ordinates will be for P and the other one for Q.
hope u understood :)
 
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ok to find co-ordinates of Q u have to solve the equation of the curve and the equation of the normal simultaneously. if u do that one of ur co-ordinates will be for P and the other one for Q.
hope u understood :)
if u dont mind cud u plz do it..coz thats wat i did but wasnt getting the ans n that other question in the other post q10(iii)
 
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if u dont mind cud u plz do it..coz thats wat i did but wasnt getting the ans n that other question in the other post q10(iii)
eqn of curve:
y= 4x - (x^2 / 2) + 3
eqn of normal :
y = -x/2 + 10
so,
-x/2 + 10 = 4x - x^2 / 2 + 3 , multiply everything by 2
-x + 20 = 8x - x^2 + 6
x^2 - 9x +14 =0
x^2 - 7x -2x + 14 =0
x(x-7) - 2(x-7) = 0
(x-2)(x-7) = 0
x= 2 or 7
when x =7
y= -7/2 +10 = 6.5 , hence Q (7,6.5)
when x=2
y = -2/2 +10 = 9, hence P (2,9)
 
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eqn of curve:
y= 4x - (x^2 / 2) + 3
eqn of normal :
y = -x/2 + 10
so,
-x/2 + 10 = 4x - x^2 / 2 + 3 , multiply everything by 2
-x + 20 = 8x - x^2 + 6
x^2 - 9x +14 =0
x^2 - 7x -2x + 14 =0
x(x-7) - 2(x-7) = 0
(x-2)(x-7) = 0
x= 2 or 7
when x =7
y= -7/2 +10 = 6.5 , hence Q (7,6.5)
when x=2
y = -2/2 +10 = 9, hence P (2,9)
k thanx(y)
 
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Iffat
i hope this answers ur question for number 10 on the other ppr. where c is the x co-ordinate of the vertex.
img_20120502_080038-1-jpg.7943
 
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I have almost tried this several times but then I give up..Help me

This question is for a cricket fan :p you need to know that only those innings get counted in which a batsmen bats and gets out.

65 Total matches..

Innings he got to bat .. 65-16 = 49

Innings in which he got out = 49 - 9 = 40

His old average was 47 .. so he scored 47*40 runs = 1880 runs

he got out on 129 in his next inning (41st Out) .. (1880+129)/41 = 49

His new average is 49.

Check the answer
 
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This question is for a cricket fan :p you need to know that only those innings get counted in which a batsmen bats and gets out.

65 Total matches..

Innings he got to bat .. 65-16 = 49

Innings in which he got out = 49 - 9 = 40

His old average was 47 .. so he scored 47*40 runs = 1880 runs

he got out on 129 in his next inning (41st Out) .. (1880+129)/41 = 49

His new average is 49.

Check the answer
The answer for this one is absolutely correct and Igot how u did it!!thanks a ton friend!!I forgot to take -9....
 
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