Mathematics: Post your doubts here!

[yuliana95]

Hi... I am learning Pure Maths 2&3 now, chapter 19(Differential Eqn). I have this question I can't seem to get it right:
Find the general solution of the differential equations:
(a) 4+x(dy/dx)=y^2

The answer key says that:
y=2(1-kx^4)/(1+kx^4) while my answer is y=2(1+kx^4)/(1-kx^4)

Please tell me what is wrong.. Any help is appreciated

 

[ni2005]

assalamualaikum!! can u please help me with this?
given the differential equation:
dH/dt = (100-H)^3
solve the differential equation, given tht H=101 when t=0, giving H in terms of t.

my answer is: H= 100+ (1/(2t+1)^0.5), i've taken negative square root, becasue then when t=0, H=101, but the answer in the marking scheme is H= 100- (1/(2t+1)^0.5), wheret=0 will give H=99.
jazaakallah

 

[ni2005]

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Hi... I am learning Pure Maths 2&3 now, chapter 19(Differential Eqn). I have this question I can't seem to get it right:
Find the general solution of the differential equations:
(a) 4+x(dy/dx)=y^2

The answer key says that:
y=2(1-kx^4)/(1+kx^4) while my answer is y=2(1+kx^4)/(1-kx^4)

Please tell me what is wrong.. Any help is appreciated

i'm getting the answer u got too, mayB it's just a printing error in the answer key

 

[Dug]

assalamualaikum!! can u please help me with this?
given the differential equation:
dH/dt = (100-H)^3
solve the differential equation, given tht H=101 when t=0, giving H in terms of t.

my answer is: H= 100+ (1/(2t+1)^0.5), i've taken negative square root, becasue then when t=0, H=101, but the answer in the marking scheme is H= 100- (1/(2t+1)^0.5), wheret=0 will give H=99.
jazaakallah

Walaikum AsSalam wr wb!

dH/dt = (100 - H)³
⌡1/(100 - H)³ dH =⌡ dt
1/(-2)(-1)(100 - H)² = t + c

When H = 101, t = 0
1/2(100 - 101)² = c
c = 1/2

1/2(100 - H)² = t + 1/2
Rearrange and take square root and you get H = 100 - √1/(2t + 1)

 

[ni2005]

Walaikum AsSalam wr wb!

dH/dt = (100 - H)³
⌡1/(100 - H)³ dH =⌡ dt
1/(-2)(-1)(100 - H)² = t + c

When H = 101, t = 0
1/2(100 - 101)² = c
c = 1/2

1/2(100 - H)² = t + 1/2
Rearrange and take square root and you get H = 100 - √1/(2t + 1)

hehehe! i've been able to work it out up to here, but i think when we take square root, we will have to take the negative, because if u replace for t=0 in your answer, H will be 99, not 101

 

[Dug]

hehehe! i've been able to work it out up to here, but i think when we take square root, we will have to take the negative, because if u replace for t=0 in your answer, H will be 99, not 101

I am assuming H is the height, right? Could you write the whole statement? Your answer seems correct if you put it like that but I still think there is a reason for the answer in markscheme.

 

[ni2005]

I am assuming H is the height, right? Could you write the whole statement? Your answer seems correct if you put it like that but I still think there is a reason for the answer in markscheme.

In an industrial process, a control mechanism supplies heating and cooling in such a way that the temperature H and the time t (each measured in suitable units) are related by the differential equation:
dH/dt = (100 - H)³

 

[Dug]

In an industrial process, a control mechanism supplies heating and cooling in such a way that the temperature H and the time t (each measured in suitable units) are related by the differential equation:
dH/dt = (100 - H)³

I think your answer is correct. The markscheme is wrong..

 

[ni2005]

I think your answer is correct. The markscheme is wrong..

only for the value t=0 that only one solution is correct, if we replace t by any other value, then the value of H obtained will satisfy both solutions

 

[Dug]

only for the value t=0 that only one solution is correct, if we replace t by any other value, then the value of H obtained will satisfy both solutions

How so? We get different values of H from both equations...

 

[ahmad0007]

AOA i need as tropical p1 and m1 past papers ............ any help???

 

[ahmad0007]

maths a levels tropical pastpapers p1.... needed .... any help

 

[felicia tan]

need help here. How to do 8 iii)? How can I integrate −20 +(2000)/(10 − h)(10 + h) ??

http://papers.xtremepapers.com/CIE/...AS Level/Mathematics (9709)/9709_w08_qp_3.pdf

 

[felicia tan]

need help here. How to do 8 iii)? How can I integrate −20 +(2000)/(10 − h)(10 + h) ??

http://papers.xtremepapers.com/CIE/...AS Level/Mathematics (9709)/9709_w08_qp_3.pdf

 

[CIE xams]

pls help me in solving thesse permutations and cmbinations questions

1.In how many ways can 8 similar balls be placed in three diffrent boxes when each box contains at least 1 ball...
ans: 21
2.if 8 balls to b selected from 3 balls of different colours, balls of each colour being availbale unlimited no. of times.total no. of selection is:
45
3.no. of ways in which 4 letters of the word MATHEMATICS can be arranged:
ans:2454
4. no. of squares on a chessboard:
ans: 204(i know this cud be done as 1^2+2^2+3^2+....8^2, but pls explain how to do it in terms of permutations or combinations)
PLS HELP FAAAAST ANYONE PLSSSSSSS....

 

[Norton]

Can u please give me the answer for this statistics 1 question

Give an example for a statement of Fact and write down the data that could be extracted from it. What are the variables in your data? Point out a qualitative variable, a discrete variable in your data and state whether they assume continuous values or discrete values.

 

[Anonimous12345]

Salams. I'm starting this year my AS in Maths and it happens that im still confused about some issues in surds and indices.
So can someone plz help me out

2 +

16

 

[Anonimous12345]

GetAttachment.jpg

 

[Anonimous12345]

C:\Users\Zara\Desktop\GetAttachment.jpg

 

[Anonimous12345]

the cubic root of 2 + the cubic root of 16
Thats my doubt. Plz help. thks