the equation of the chord of contact of the pair of tangents drawn to the ellipse `4x^2+9y^2=36` from the point `(m ,n)` where `mdotn=m+n ,m ,n` being nonzero positive integers, is `2x+9y=18` (b) `2x+2y=1` `4x+9y=18` (d) none of these