Comment on the style of this C++ class for a 2D Vector
This looks pretty good! I don't think you need to change much, but there are some things missing that you will likely need:


normalize() or normal() method to either normalize a vector or return a normalized version of the vector. If you're doing physics, you'll need normalized vectors for lots of operations, probably.
Scalar multiply (operator*(const T)). You'll likely need to scale vectors frequently and will do that by multiplying by a scalar.
operator==() and/or operator!=(). You should define one in terms of the other.
Possibly a squared magnitude. Sometimes taking the square root in the Magnitude() function is a bottleneck and you don't need it (for example to see if a point is within a given radius of another point). It can be faster to get the squared magnitude of the vector between the two points if that's something you do a lot.