The Student Room Group

differentiation question

differentiate with respect to t: (β/(β-t))^α

I get
α*β^α / (β-t)^(α+1)

Is that correct? The method used by the textbook is different: they've done (see image) whereas I got the (β-t))^α in the numerator and then used the chain rule diff.jpg
Original post by zomgleh
differentiate with respect to t: (β/(β-t))^α

I get
α*β^α / (β-t)^(α+1)

Is that correct? The method used by the textbook is different: they've done (see image) whereas I got the (β-t))^α in the numerator and then used the chain rule diff.jpg


They both work out the same, and they're both missing a minus sign.
(edited 11 years ago)
Reply 2
Original post by ghostwalker
they're both missing a minus sign.


how come? I was almost sure the textbook solution would be correct?
Original post by zomgleh
how come? I was almost sure the textbook solution would be correct?


My mistake! Grovel, grovel!

I was confusing the alpha exponent in the numerator, with the one in the denominator.
(edited 11 years ago)
Reply 4
Original post by ghostwalker
My mistake! Grovel, grovel!

I was confusing the alpha exponent in the numerator, with the one in the denominator.


haha phew! thanks anyway, you've helped me way too many times, appreciate it!
Reply 5
Original post by ghostwalker
My mistake! Grovel, grovel!

I was confusing the alpha exponent in the numerator, with the one in the denominator.


Ok so I've done this one before but looking back at it I can't seem to figure it out-- dy/dx of y=(x-y)^3
answer is 3(x-y)^2 / (1+ 3(x-y)^2
Original post by zomgleh
Ok so I've done this one before but looking back at it I can't seem to figure it out-- dy/dx of y=(x-y)^3
answer is 3(x-y)^2 / (1+ 3(x-y)^2


Treat it with the chain rule. What do you get for your first line of working?
Reply 7
Original post by ghostwalker
Treat it with the chain rule. What do you get for your first line of working?


I get 3(x-y)^2
Original post by zomgleh
I get 3(x-y)^2


You had y=(x-y)^3

So, using the chain rule we get y=3(xy)2(1y)y'=3(x-y)^2(1-y')

Make sure you understand it, and then just rearrange.
Reply 9
Original post by ghostwalker
You had y=(x-y)^3

So, using the chain rule we get y=3(xy)2(1y)y'=3(x-y)^2(1-y')

Make sure you understand it, and then just rearrange.


got it, you have once again saved the day! voted you for the most helpful member btw, seeing as I probably won't be able to answer any of your doubts :P

Quick Reply

Latest