Calculus

Please let me know the moethod for answering the questions and what answers you get and how you got them. i want to check them as well with my answers. struggling a lot with question 2 a lot..can barely answer it..
thanks so much

Calculus.jpg126.0KB

Reply 1

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Get me off the £\?%!^@ computer

Original post by Stewww

What have you done?

I did a sketch and then did the integral in two parts. I'll tell you if you're right if you post your answer.

Reply 2

Stewww

Original post by Get me off the £\?%!^@ computer

What have you done?

I did a sketch and then did the integral in two parts. I'll tell you if you're right if you post your answer.

um ok for question 1ai) i got 0.8

for 1aii) i got 3

for 1b) i got 1/(x+y)

and for 1c) i got 3

can't answer question 2 :/

Reply 3

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Get me off the £\?%!^@ computer

Ha. I thought you wanted help with q2. That's what my post related to. For 2b I changed the order of integration.

I agree with your first two answers. You could check these using WolframAlpha btw.

I'll look at the next one now.

(edited 13 years ago)

Reply 4

Stewww

i don't really understand how to use wolframalpha. :s-smilie:

yeh i need help with q2..i haven't been able to answer it :colondollar:

so sorry for being dumb :colondollar:

so question 1 is correct, or you agree with the answers i got?

Reply 5

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Get me off the £\?%!^@ computer

WolframAlpha couldn't be much easier. Just type in what you want, using a tiny bit of common sense.

http://www.wolframalpha.com/input/?i=limit+x-%3E5+%28x^2-2x-15%29%2F%28x^2-25%29

I didn't get 1/(x+y) for part c. You're close though.

Edit. Put in a missing word.

(edited 13 years ago)

Reply 6

Stewww

Original post by Get me off the £\?%!^@ computer

ok i still don't understand how i can put question 1c into wolfram, or question 2 ):

Reply 7

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Get me off the £\?%!^@ computer

I just tried a few things and got this.

http://www.wolframalpha.com/input/?i=partial++w.r.t.+y+%28+xlog%28x%2By%29+%29

You could do most of part c on there too.

Just try. :smile:

Anyway that's only for checking.

Post your working and someone will check.

What did you get for the tangent plane and the directional derivative?

Reply 8

Stewww

Original post by Get me off the £\?%!^@ computer

I just tried a few things and got this.

http://www.wolframalpha.com/input/?i=partial++w.r.t.+y+%28+xlog%28x%2By%29+%29

You could do most of part c on there too.

Just try. :smile:

Anyway that's only for checking.

Post your working and someone will check.

What did you get for the tangent plane and the directional derivative?

here's what i did for 1b)

dunno how to do 1c and question 2 ):

but thank you for your help!!

Image 0017.jpg66.4KB

Reply 9

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Get me off the £\?%!^@ computer

Original post by Stewww

here's what i did for 1b)

dunno how to do 1c and question 2 ):

but thank you for your help!!

Your mistake is in

\frac{\partial^2 z}{\partial y^2}

When you differentiated x w.r.t y you should have writen 0.

As for 1c) Remind yourself of the equaton of the tangent plane. It's in your notes, isn't it?

Reply 10

Stewww

Original post by Get me off the £\?%!^@ computer

Your mistake is in

\frac{\partial^2 z}{\partial y^2}

When you differentiated x w.r.t y you should have writen 0.

As for 1c) Remind yourself of the equaton of the tangent plane. It's in your notes, isn't it?

hmmm :/
i think i did do that..i'm still getting d^2z/dy^2 as 1/(x+y) + x/(x+y)^2

:/

Reply 11

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Get me off the £\?%!^@ computer

Original post by Stewww

hmmm :/
i think i did do that..i'm still getting d^2z/dy^2 as 1/(x+y) + x/(x+y)^2

:/

So you're differentiating

\frac{x}{x+y}

x(x+y)^{-1}

(which ever way you prefer to look at it) with respect to y.

In your working you have just written down your answer. That's fine as long as you get it right. It's not coming out right so break it down into smaller steps. If you like, post your working again. If you do it in enough detail you will not even need to post it, because you will get it right.