<a href="http://www.codecogs.com/eqnedit.php?latex=\textup{Equation of tangent is }x@plus;y(b-4)^2=2b-4\\ \textup{Passes through the origin, therefore 0,0 satisfies this:}\\ 0@plus;0(b-4)^2=2b-4\\ b=2 \textup{ Sub back into tangent:}\\ x@plus;y(2-4)^2=2(2)-4\\ x@plus;4y=0 \\ \textup{Use a...