If you want to get u substitution for ths integrals draw a curve
y^2=ax^2+bx+c
and cut it with secant line
If secant line intersects curve at
(λ,0)
or
(μ,0)
you will get third substitution
If secant line intersects curve at
(0,\sqrt{c})
or
(0,−\sqrt{c})
you will get second substitution
Assume...