Intergration by Substitution

val1

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Oct 17, 2005
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Please can you help me with this question?

Evaluate this definite integral by using some suitable substitution


\(\displaystyle \L

\int_{{\textstyle{\pi \over 6}}}^{{\textstyle{\pi \over 3}}} {\tan ^2 x\sec ^2 x{\rm }dx}\)


\(\displaystyle \L

let{\rm }u = \tan x{\rm }du = \sec ^2 x{\rm }dx\)

\(\displaystyle \L

so,\int_{{\textstyle{\pi \over 6}}}^{{\textstyle{\pi \over 3}}} {u^2 du} = \frac{1}{3}u^3 = \frac{1}{3}\left[ {\tan ^3 x} \right]_{{\textstyle{\pi \over 6}}}^{{\textstyle{\pi \over 3}}}\)

\(\displaystyle \L

= \frac{1}{3}\left[ {3\sqrt 3 - \frac{{\sqrt 3 }}{9}} \right] = \frac{{26\sqrt 3 }}{{27}}\)

Can you tell me if this is the correct answer?
:?:
 
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