Math Is Fun Forum

LuisRodg

Real Member

Registered: 2007-10-23

Posts: 322

Just finished my first Calculus II test.....

Well I just got out of my test and I have some doubts pertaining to some questions.

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I tried many forms of u-substitutions and I wasnt able to get it...

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Find the surface area of the revolution of the function f(x) around the y-axis from x=0 to x=2.

i wasnt sure if I had to use dx or dy....I tried it both ways and I wasnt able to solve the integral obtained. Tried many u-substitutions etc and nothing.

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And the third one was:

Do you split this from 0 to PI/6 and from PI/6 to PI/2?

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Each of this questions were worth 10 points....Ouch. Hope he curves.

Last edited by LuisRodg (2008-02-11 05:27:33)

mathsyperson

Moderator

Registered: 2005-06-22

Posts: 4,900

Re: Just finished my first Calculus II test.....

Not sure if it's the intended method for the first one, but if you're a bit sneaky you can get partial fractions out of it:

You can then integrate those two terms separately.

You're correct for the third one:

And I don't remember calculus enough to help you with the second. :|

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Why did the vector cross the road?
It wanted to be normal.

LuisRodg

Real Member

Registered: 2007-10-23

Posts: 322

Re: Just finished my first Calculus II test.....

Thanks Mathsy.

For the second one here is the formulas you use:

or

Like I said, I was sure which one I had to use?

I tried them both but the resulting integral from that formula was way too complicated or at least I couldnt solve it.

Last edited by LuisRodg (2008-02-11 09:29:30)

LuisRodg

Real Member

Registered: 2007-10-23

Posts: 322

Re: Just finished my first Calculus II test.....

Could anyone please help me with the Surface Area one?