How do you integrate sec2x tan2x dxsec2xtan2xdx?

1 Answer
Feb 21, 2015

I would write the integral as:

intsec(2x)tan(2x)dx=int1/cos(2x)sin(2x)/cos(2x)dx=sec(2x)tan(2x)dx=1cos(2x)sin(2x)cos(2x)dx=

we can see that:

d[cos(2x)]=-2sin(2x)dxd[cos(2x)]=2sin(2x)dx
and so:
sin(2x)dx=(d[cos(2x)])/-2sin(2x)dx=d[cos(2x)]2

with this in mind I write the integral as:

int1/cos^2(2x)*1/-2d[cos(2x)]=1cos2(2x)12d[cos(2x)]=
=1/-2intcos^(-2)(2x)d[cos(2x)]==12cos2(2x)d[cos(2x)]= (treating cos(2x)cos(2x) as if it were xx in a normal integration where you get x^(n+1)/(n+1)xn+1n+1)
=1/2*1/cos(2x)+c=121cos(2x)+c