this might be a bit hard to understan but ill give a shot
the only thing relatin sectheta and tantheta is the identity 1+(tantheta)^2=(sectheta)^2
x-1=2tantheta
(x-1)^2=4(tantheta)^2
(x-1)^2/4=(tantheta)^2
((x-1)^2/4)+1=(tantheta)^2+1 ....(1)
y=3sectheta-4
y+4=3sectheta
(y+4)^2=9(sectheta)^2...