If the equation ax2+2hxy+by2+2gx+2fy+c=0represents a pair of parallel lines ba=
gf
g2f2
f2g2
fg
The condition that the equation ax2+2hxy+by2+2gx+2fy+c=0 represents pair of parallel lines is h2=ab, and af2=bg2Rewrite the second condition as f2g2=baTherefore ba=f2g2