integral of sqrt(x^2+1) with trig sub: https://www.youtube.com/watch?v=O6i5zeoIlsM
wikipedia Euler Sub: https://en.wikipedia.org/wiki/Euler_substitution
integral of sqrt(1+x^2), integral of sqrt(1+x^2),
integral of sqrt(x^2+1), with Euler's Substitution for integrals,
blackpenredpen,
math for fun