Find xy ; when x2+6y2=5xy.
Divide through by y2
(xy)2+6=5(xy)
Let xy=z
z2−5z+6=0
(z−2)(z−3)=0
⇒z=2 or 3
ie,xy=2 or 3
(x+4)2−5xy−20y−6y2=