Volume

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(edited 4 years ago)

A solid formed by rotating the curve y = x^2 +4 between x =1 and x =t, t>1, through 360 degrees about y-axis. Find the value of t for the volume of solid formed is 40pi

Where have I gone wrong?

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Haven't checked the whole thing so it could be elsewhere, but it may be your limits of integration. You correctly have an upper limit of t² + 4, which is what y comes to when x = t. But what about when x = 1, the lower limit?

Reply 2

Pangol

Original post by ottersandseals1

Yeah I forgot to put that in

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Has that given you the right answer? You'll understand that I'm not inclined to check every line unless you're still having problems.

Reply 3

ottersandseals1

Original post by Pangol

Has that given you the right answer? You'll understand that I'm not inclined to check every line unless you're still having problems.

I don't know what the answer is

Reply 4

Pangol

Original post by ottersandseals1

I don't know what the answer is

In that case, how did you know you weren't right the first time?!

Just had a closer look at your working. It doesn't appear that you have actually done any integration.

Reply 5

Pangol

Original post by ottersandseals1

I don't know what the answer is

Just checked the answer - you will know you probably have it right if it comes out as an integer.

Reply 6

Pangol

Original post by ottersandseals1

is it 2.5?

Not what I got (and not an integer!). Quite possible I made a slip, I grant you.

But do you see what I mean about you now having actually integrated?