The problem is to find the integration of sqrt(x^2 + 16) .
I have been using x=4tan θ for the substitution and dx=4sec^2 θ .
Please show your work.
if that is the case, then you should have worked your original substitution down to this point ...
let's ignore the constant (16) for a bit and focus effort on the integral of secant cubed. using integration by parts ...
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put the constant (16) back ...
I'll leave you the task of back substituting.