• We need your support!

    We are currently struggling to cover the operational costs of Xtremepapers, as a result we might have to shut this website down. Please donate if we have helped you and help make a difference in other students' lives!
    Click here to Donate Now (View Announcement)

Mathematics: Post your doubts here!

Dudu

Dudu

Messages
85
Reaction score
58
Points
28
In all math papers, you know how it says on the first page... always give answers to 3SF unless stated otherwise?

Can you lose marks for the Final answer (A1) if you dont?
 
Esme

Esme

Messages
681
Reaction score
438
Points
73
Dudu said:
In all math papers, you know how it says on the first page... always give answers to 3SF unless stated otherwise?

Can you lose marks for the Final answer (A1) if you dont?
Click to expand...

Definitely!! It's very important to give your ans to 3 S.F unless stated otherwise
 
A

abbey789

Messages
66
Reaction score
12
Points
18
freezingfires said:
Here it says the rate of increase of the surface area of the sphere is proportional to its volume.
so dA/dt=kV
dA/dt=4pi r^2 differentiating this gives us 8pir dr/dt
now equate
8pirdr/dt=k(4/3pi r^3)
put values of dr/dt and r given in the question to get k=12/25
Now put this value of k back in 8pirdr/dt=k(4/3pi r^3) to get dr/dt=0.08r^2
Now apply differential equation solve it and you will get
-1/r=0.08t+k
put t=o and r=5 to get k=-1/5
Now solve it further to get in terms of r and t
your final equation will be r=5/(1-0.4t)
for the last part equate the denominator to 0 you will get t=2.5 which means that if denominator is 0 equation is not valid so values of t must be grater than 0 but less than 2.5.HOPE YOU GOT IT!! PLEASE PRAY FOR ME!! :)
Click to expand...
THANK YOU SO MUCH! Yes I will! :)
I didn't get this part dA/dt=4pi r^2 differentiating this gives us 8pir dr/dt
 
VinnCh

VinnCh

Messages
12
Reaction score
6
Points
3
LMGD33 said:
Hello guys, I'm solving http://papers.xtremepapers.com/CIE/Cambridge International A and AS Level/Mathematics (9709)/9709_s12_qp_33.pdf and I had this beautifully posted solutions to all the paper, i', just wondering in Question 5 (ii) How did they get that formula? Why did they divide by 70 and multiply by 100? Thank you so much!!
View attachment 26637

Credit to Anika Raisa
Click to expand...

After I went through the question. The initial mass (t=0) of substance B, which is also y is 70. The question asks for percentage mass remaining. Since the mass remaining as t increase to infinite is 70/e, the percentage mass remaining should be (remaining/initial) x 100 , which is also [(70/e)/70]x100.
I hope you understand it. =)
 
VinnCh

VinnCh

Messages
12
Reaction score
6
Points
3
LindaKim123 said:
http://papers.xtremepapers.com/CIE/Cambridge International A and AS Level/Mathematics (9709)/9709_w12_qp_31.pdf

question 9 ii) please!!
Click to expand...
Since 1+√2i and 1-√2i are the two imaginary roots, which means x=1+√2i and x=1-√2i . Equate them, ( x - [1+√2i] ) ( x - [1-√2i] ) and expand them. Use the resulting equation ( x^2 -2x + 3 ) to do long division with P(x). You'll get a quadratic equation in return, then just use the usual way to find the roots. =)
 
You must log in or register to reply here.
Top