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# C3 Product Rule Help watch

1. Hey, i was looking for an insight into where ive gone wrong on the folllowing question:

Differentiate y=(x+2)e-x

i did the product rule and got
Y=uv

u= x+2
du/dx= 1

v= e-x
dv/dx= -e-x

so dy/dx= e-x + -e-x(x+2)

but the mark scheme says its
-e-x(x+1)

thanks for the read, any help is appreciated
2. (Original post by TheGreat1)
Hey, i was looking for an insight into where ive gone wrong on the folllowing question:

Differentiate y=(x+2)e-x

i did the product rule and got
Y=uv

u= x+2
du/dx= 1

v= e-x
dv/dx= -e-x

so dy/dx= e-x + -e-x(x+2)

but the mark scheme says its
-e-x(x+1)

thanks for the read, any help is appreciated
Your answer is correct - you should simplify it down. Can you see a factor which you can take out?

EDIT: Maybe not. -e^-x(x+2) - this bit isn't right.
EDIT2: Gah shutup Blazy.
3. (Original post by TheGreat1)
Hey, i was looking for an insight into where ive gone wrong on the folllowing question:

Differentiate y=(x+2)e-x

i did the product rule and got
Y=uv

u= x+2
du/dx= 1

v= e-x
dv/dx= -e-x

so dy/dx= e-x + -e-x(x+2)

but the mark scheme says its
-e-x(x+1)

thanks for the read, any help is appreciated
What happens when you take out the common factor of
4. (Original post by TheGreat1)
Hey, i was looking for an insight into where ive gone wrong on the folllowing question:
You can check that your answer is correct or otherwise by using your calculator. Set x = 1.5 or something and see what happens.

There is usually no need for YOUR answer to look exactly like the answer in the mark scheme.
5. (Original post by TenOfThem)
What happens when you take out the common factor of
the you should get -e-x(-1+(x+2))?

if thats correct then theres the answer
6. (Original post by TheGreat1)
the you should get -e-x(-1+(x+2))?

if thats correct then theres the answer
and -1+x+2 =
7. (Original post by TenOfThem)
and -1+x+2 =
alrighty, thanks for yours (and everyone elses) help
8. (Original post by TheGreat1)
alrighty, thanks for yours (and everyone elses) help
NP

As Steve said ... your answer would have been accepted unless there was a format specified in the question
9. Its because the next question asked for d2y/dX2 so doing it in this format would have made the next part easier.
10. (Original post by TheGreat1)
Its because the next question asked for d2y/dX2 so doing it in this format would have made the next part easier.
ahhhhh

I usually factorise if I can anyway

it helps if you need to find turning points and/or differentiate again

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