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C3 Differentiation

Hey guys,

I'm having trouble with this question. Usually I can work it out but I need help on this occasion :frown:

y = (x-4)ln(4-x)

1) Differentiate Y.

2) Find value of X in terms of e.

I tried working it out and got: ln(4-x) which can't be right.
Original post by Iceyy
Hey guys,

I'm having trouble with this question. Usually I can work it out but I need help on this occasion :frown:

y = (x-4)ln(4-x)

1) Differentiate Y.

2) Find value of X in terms of e.

I tried working it out and got: ln(4-x) which can't be right.

post dat working
Reply 2
Avatar for advice_guru
advice_guru
Original post by Iceyy
Hey guys,

I'm having trouble with this question. Usually I can work it out but I need help on this occasion :frown:

y = (x-4)ln(4-x)

1) Differentiate Y.

2) Find value of X in terms of e.

I tried working it out and got: ln(4-x) which can't be right.


Use product rule on y=(x-4)ln(4-x)
Reply 3
Avatar for Iceyy
Iceyy
OP
Original post by Felix Felicis
post dat working


Okay, I used the Product Rule so that:

U = x-4 Du = 1
V = ln(4-x) Dv = -1/(4-x)

V x Du + U x Dv

ln(4-x) + (x-4) x -1/(4-x)

= ln(4-x) + (-x+4)/(4-x)

=ln(4-x) + 1!!!

Edit: OH DEAR!!! Classic mistake. I forgot to add 1 at the end -.-

Sorry guys, me being stupid.
(edited 11 years ago)
Reply 4
Avatar for MOTORMADX
MOTORMADX
9
Original post by Iceyy
Hey guys,

I'm having trouble with this question. Usually I can work it out but I need help on this occasion :frown:

y = (x-4)ln(4-x)

1) Differentiate Y.

2) Find value of X in terms of e.

I tried working it out and got: ln(4-x) which can't be right.

multiply the brackets out, then you should get xln[4-x] and -4ln[4-x] then use the product rule on xln[4-x] and do normal differentaiting on the -4ln[4-x] , i might not be right, this is me just briefly guessing, hope i helped you. :smile:

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