Author Topic: what am i doing wrong? (Read 3031 times) Tweet Share

Hooligan · « **Reply #15 on:** October 15, 2009, 09:46:23 pm »

In fact, there is never a 1/2 in front of the intergral....

$\int_{0}^{\frac{\pi }{8}}\sec^{2}(2x)e^{2tan(2x)} dx$

$\int_{0}^{1}\ e^{2u} du$

kamil9876 · « **Reply #16 on:** October 15, 2009, 09:46:44 pm »

lol i didn't really care about the constant since when i help ppl on integration i always omit constants since they are trivial and just briefly show them how to do the juicy bits. Plus i invested some trust in that $\frac{1}{4}$ that nels wrote. Anyways, a bit hypocritical given that i said "precise".

Flaming_Arrow · « **Reply #17 on:** October 15, 2009, 09:48:09 pm »

Quote from: Hooligan on October 15, 2009, 09:46:23 pm

In fact, there is never a 1/2 in front of the intergral....

$\int_{0}^{\frac{\pi }{8}}\sec^{2}(2x)e^{2tan(2x)} dx$

$\int_{0}^{1}\ e^{2u} du$

shouldnt there be a 1/2 at the front?

kamil9876 · « **Reply #18 on:** October 15, 2009, 09:50:37 pm »

yes, thereshould be a 1/2 instead of 1/4. This is beause $\frac{du}{dx}=2sec^2(2x)$ and so 1/2 cancels 2.

TrueTears · « **Reply #19 on:** October 15, 2009, 09:51:03 pm »

$\int_{0}^{\frac{\pi }{8}}\sec^{2}(2x)e^{2tan(2x)} dx$

So let $u = tan(2x)$

$\frac{du}{dx} = 2sec^2(2x)$

$du = 2sec^2(2x)dx$

$\implies \frac{1}{2} \int_0^1 e^{2u} du$

Hooligan · « **Reply #20 on:** October 15, 2009, 09:54:59 pm »

Quote from: nels on October 15, 2009, 09:22:58 pm

hmmm...did that but still ended up with $\frac{1}{4}(e^{2}-1)$

hmmm... but that is the right answer if you check with a calculator.... weird... maybe the book is wrong?

kamil9876 · « **Reply #21 on:** October 15, 2009, 09:57:02 pm »

TT's integral evaluates to that, that is correct. another factor of 1/2 comes from antidiff hence the 1/4.

nels · « **Reply #22 on:** October 15, 2009, 10:03:52 pm »

yes, the book is wrong. just checked the assessment report. should've thought of that an hour ago lol. sorry guys.

thanks all.

Hooligan · « **Reply #23 on:** October 15, 2009, 10:19:13 pm »

Quote from: nels on October 15, 2009, 10:03:52 pm

yes, the book is wrong. just checked the assessment report. should've thought of that an hour ago lol. sorry guys.

thanks all.

haha... xD Its mind boggling to how they could get it wrong, when all they are doing (or rather, should be doing) is copying the answers straight from the assessor's report. =P Its seems trivial as all our teachers tend to say, however it isn't soo trivial when even a printing company gets it wrong, is it? haha. xD

TrueTears · « **Reply #24 on:** October 15, 2009, 10:21:19 pm »

Quote from: Hooligan on October 15, 2009, 10:19:13 pm

Quote from: nels on October 15, 2009, 10:03:52 pm
yes, the book is wrong. just checked the assessment report. should've thought of that an hour ago lol. sorry guys.

thanks all.

haha... xD Its mind boggling to how they could get it wrong, when all they are doing (or rather, should be doing) is copying the answers straight from the assessor's report. =P Its seems trivial as all our teachers tend to say, however it isn't soo trivial when even a printing company gets it wrong, is it? haha. xD

Same for physics checkpoints...

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