Help me solve this integral

X^2+16=0
X=4i
X1=-4i
Then you will get
16+x^2=(x+4i)*(x-4i)
Now replace the complex number by its euler substitution and you should get a sinousoidial function inside the square root

Both wrong

That advice is pointless 12^2+4 is obviously something you shouldnt approximate in this case

Correct and coincides with OP's final answer

why would someone who looks like a 1st year engineering undergrad be doing riemann sums

Whats the sqrt(16 + x^2)?