Question asks:
Find the volume of the solid bounded by: z = 4x^2 + y^2 and the cylinder y^2+z=2
In the solution they used change of variable by putting in x = r cosθ/sqrt 2 and
y = r sin θ, z = z
this looks like cylindrical co ordinates to me, but I thought that you always use
x = r cos θ
can someone explain why divide it by root 2? And how can you just look at questions like these and decide what change of variable to make? I'm really confused.