`inttsec^2(2t)dt`
If f(x)
and g(x) are differentiable functions, then
`intf(x)g'(x)dx=f(x)g(x)-intf'(x)g(x)dx`
If we write f(x)=u and
g'(x)=v, then
`intuvdx=uintvdx-int(u'intvdx)dx`
Now using
the above method of integration by parts,
`inttsec^2(2t)dt=tintsec^2(2t)dt-int(d/dt(t)intsect^2(2t))dt`
`=t*tan(2t)/2-int(1*tan(2t)/2)dt`
`=1/2t*tan(2t)-1/2inttan(2t)dt`
Now let's evaluate `inttan(2t)dt` by
using the method of substitution,
Substitute `x=cos(2t),=>dx=-2sin(2t)dt`
`inttan(2t)dt=int(sin(2t)/cos(2t))dt`
`=intdx/(-2x)`
`=-1/2ln|x|`
substitute back `x=cos(2t)`
`=-1/2ln|cos(2t)|`
`inttsec^2(2t)dt=1/2t*tan(2t)-1/2(-1/2ln|cos(2t)|+C`
C is a
constant
`inttsec^2(2t)dt=1/2t*tan(2t)+1/4ln|cos(2t)|+C`
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