#x = r cos theta, y = r sin theta#
#(5x - 7y)^2 - y + x = 6#
#"Substituting values of x & y in terms of " r and theta#,
#(5 r cos theta - 7 r sin theta)^2 - r sin theta + cos theta = 6#
#25r^2 cos^2 theta + 49 r^2 sin^2 theta - 70 r^2 cos theta sin theta - r sin theta + r cos theta = 6#
#25 r^ cos^2 theta + 25 r^2 sin^2 theta + 24 r^ sin^2 theta - 70 r^2 cos theta sin theta - r sin theta + r cos theta = 6#
#25 + 24 r^2 sin^2 theta - 70 r^2 cos theta sin theta - r sin theta + r cos theta = 6#
#2r^2 sin theta (12 sin theta - 35 cos theta ) + r (cos theta - sin theta) + 19 = 0#