I've had a crack at the first 2. I'm not sure though
I solved the equation for y to get x and got 4 and -4.
Therefore A is (-4,0) and B is (4,0)
For the second part I used the distance formula... and got 8.
For the 3rd part... I'm thinking to use dy/dx........
When I use it, I then put in -4 for the x value to get the deepest point