Maths & Physics problem!

Imagine that I have a ball moving with velocity of (0,-2) and hit’s a plane with hitnormal of (1,1).
How would i calculate the ball’s velocity after the hitting?

I believe that dot product might help but I suck at vector products and I have no idea how to use them.

This is really bugging me :confused:

This probably isn’t the way it should be done, but :

I just solved it with help of Martijn & Andreas!

NewVel = Vel - 2*Velocity:Dot(HitNormal)*HitNormal