Thread: Analytic Geometry

Hello, everybody. I need help...
Show that, for all values of p, the point P given by x=ap², y=2ap lies on the curve y²=4ax.
a) Find the equation of this normal to this curve at the point P.
If this normal meets the curve again at the point Q (aq², 2aq). Show that p²+pq+2=0
b) Determine the coordinates of R, the point of intersection of the tangents of the curve at the point P and Q.
Hence, show that the locus of the point R is y²(x+2a) +4a³=0

I already solved Q (a) and first question of Q (b). However, I can’t solve the last question: “Hence, show that the locus of the point R is y²(x+2a) +4a³=0” in Q (b). Can somebody help me?
Thanks!!

Presumably, you have found that that has the coordinates:



Now, use the relationship between and you found earlier:



which when solved for is:



Now you may write the coordinates of as parametric equations in one parameter, which you may then eliminate to obtain the required Cartesian equation.

Hey AuXian.

I haven't seen this stuff since high school (more than 10 years) but the wiki page gives a derivation of the locus for the parabola:

Parabola - Wikipedia, the free encyclopedia

I'm not sure if you just formulas or have to derive things, but if you just formulas the wiki gives a derivation from start to finish in terms of the a term.