Created a parabola, now I need it to bounce. Uses basic projectile physics.

I've created a very basic projectile object in C#, I give it an angle and velocity... and it shoots it. I now need to figure out how to make it bounce when it hits the ground (and the wall, but that can be later). Below is the code from my update method of the projectile that is basically iterating through the algorithm to generate the new x,y coords.

I also don't really know where to check for the bounce, I imagine i do it in the front end of the form/canvas that has created the projectile instance. I'm having a hard time with the logic here. help, please!

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dt = .3f;
            gravity = 9.8f;
            this.VelocityX = (float)(this.initialVelocity * (float)Math.Cos(Angle) * t);
            this.VelocityY = (float)(this.initialVelocity * (float)Math.Sin(Angle) * t - gravity * t * t / 2);
 
            this.x = this.VelocityX + this.InitialX;
            this.y = -this.VelocityY + this.InitialY;
            
            t += dt;