parametrics qn (1 Viewer)

[blakwidow]

Can someone explain the step in bold to me?

 

[denoz]

If the roots are equal to one another that just means it is a double root .i.e. the line just touches the curve.

 

[wrxsti]

they are working with the discrimiant, becuase its a tangent, it only hits the parabola in one place, therefore there is only one root (2 of the roots are equal meaning only one root) now according to the discriminant b^2 + 4ac = 0 for equal roots (one root). hope i havnt confused u or anyting