#3=(7x-5y)^2 - y# ...............(Given equation)
Put #x=rcostheta # and #y=rsintheta# ; we get :-
#rArr3=(7rcostheta-5rsintheta)^2-rsintheta#
#rArr3=49r^2cos^2theta+25r^2sin^2theta-70r^2costheta.sintheta-rsintheta#
#rArr3=24r^2cos^2theta+(25r^2cos^2theta+25r^2sin^2theta)-70r^2costheta.sintheta-rsintheta#
#rArr3=24r^2cos^2theta+25r^2-70r^2costheta.sintheta-rsintheta#
#:.25r^2+24r^2cos^2theta-70r^2costheta.sintheta-rsintheta-3=0#
is the Polar form