• Feb 18th 2009, 09:49 PM
s3n4te
intergral(tanx(secx)^2,x)

my book tells me to make u = sec(x) du = tanxsecx dxwhich makes sense, but could you also make u = tanx making du = (secx)^2 dx? But the latter method is incorrect why?
• Feb 18th 2009, 09:54 PM
mr fantastic
Quote:

Originally Posted by s3n4te
intergral(tanx(secx)^2,x)

my book tells me to make u = sec(x) du = tanxsecx dxwhich makes sense,

but could you also make u = tanx making du = (secx)^2 dx? Mr F says: Yes. And, in my opinion, this is by far the simplest approach to take.

But the latter method is incorrect Mr F says: Says who!?

why? Mr F says: It's not incorrect. In fact, it's better!

..
• Feb 18th 2009, 09:58 PM
mollymcf2009
Quote:

Originally Posted by s3n4te
intergral(tanx(secx)^2,x)

my book tells me to make u = sec(x) du = tanxsecx dxwhich makes sense, but could you also make u = tanx making du = (secx)^2 dx? But the latter method is incorrect why?

Where did it say that the second way was incorrect? You could use either.
• Feb 18th 2009, 10:00 PM
s3n4te
When I graphed both functions they aren't the same, is that normal?
• Feb 18th 2009, 10:12 PM
mollymcf2009
Quote:

Originally Posted by s3n4te
When I graphed both functions they aren't the same, is that normal?

The area under the curves will be the same which is what you are calculating using the integral.
• Feb 18th 2009, 10:17 PM
s3n4te
oh that make sense :P

thanks