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#1 2009-10-27 19:54:06
- Identity
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- Registered: 2007-04-18
- Posts: 934
trig substitution
When finding
, using the substitution we eventually arrive atWhy do we assume
is positive here? Why don't the textbooks say it's ?Last edited by Identity (2009-10-27 19:56:14)
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#2 2009-10-27 23:15:20
- mathsyperson
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- Registered: 2005-06-22
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Re: trig substitution
I think your substitution should be x = 2sinθ instead. The second line continues as if that's the substitution you'd used.
If you're saying that cosθ needs to be positive because it's inside a root, that doesn't matter because it's being squared first. cos²θ is always positive with no assumptions required.
Why did the vector cross the road?
It wanted to be normal.
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#3 2009-10-28 01:09:21
- Identity
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- Registered: 2007-04-18
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Re: trig substitution
thanks mathsyperson
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