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Problems in Mathematical Analysis.pdf - pwp.net.ipl.pt

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Sec. 7]_Integrat<strong>in</strong>g Trigonometric Functions__129<br />

2) If m and n are even positive numbers, then the <strong>in</strong>tegrand (I) is transformed<br />

by means of the formulas<br />

s<strong>in</strong> 2 *= y (1 cos 2*), cos 2 *= y (1 + cos 2*),<br />

s<strong>in</strong> JCGOS x= s<strong>in</strong> 2*.<br />

Example 2. f cos 2 3x s<strong>in</strong> 4 3* dx = f (cos 3* s<strong>in</strong> 3*) 2 s<strong>in</strong> 2 3x dx =<br />

p s<strong>in</strong> 2 '<br />

6x1 cos 6* , 1 f . v .<br />

, , Zc 2C fi<br />

= \ ----- 2 2<br />

dx = \ (s<strong>in</strong> 6A: s<strong>in</strong> 6x cos o^) ax =<br />

1 f / 1 cos 12* . , c c \ ,<br />

= -n- = s<strong>in</strong> 3- \ 2 GA: cos 6^ dx =<br />

^> J \ ^ /<br />

x s<strong>in</strong> 12AC<br />

3) If m= [i and n= v are <strong>in</strong>tegral negative<br />

parity, then<br />

5-1900<br />

_ C<br />

J<br />

dx<br />

cos v<br />

In particular, the follow<strong>in</strong>g <strong>in</strong>tegrals reduce to this case:<br />

Example 3. f -^-= C sec 2 xd (tan *)= f (l+tan*x) d (tan x)<br />

J COS X J J<br />

= tan x-p--=- tan '* + C.<br />

8 jc + C.<br />

o<br />

_1 r<br />

numbers of identical<br />

""- -<br />

tan 2 ~

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