Evaluate: (i) `intsec^4 2x\ dx` (ii) `intcos e c^4\ 3x\ dx`

Explanation

(i)

`int sec ^{4} 2 x d x `

`int sec ^{4} 2 x d x `

`=int sec ^{2} 2 x cdot sec ^{2} 2 x d x `

`=int(1+tan ^{2} 2 x) cdot sec ^{2} 2 x d x `

`text { Let } tan 2 x=t `

`Rightarrow sec ^{2} 2 x cdot 2 d x=d t `

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