Solution:
To find the normal;
At A(y,x) but y=0
Since;
y2=4ax
⇒2ydxdy=4a
⇒dxdy=y2a
Slope of the tangent at
P(at2,2at) ;m1=dxdy=2at2a =t1
Hence slope of the normal at P is given as;
m2=t1−1 =−t
Therefore equation of the normal is given by;
y=m2x+c⇒y=−tx+c
Put x=at2,y=2at
So, c=2at+at3
Thus, tx+y=2at+at3
Hence;
y−2at=−t(x−at2)
But y=0
−2at=−tx+at3
Rewrite as;
tx=at3+2at
Divide by t,we get;
x=at2+2a
Take the midpoint of AP to be B(h,k)
Here;
h=2at2+2a+at2 =at2+a
k=20+2at =at
Since ;
y2=4ax
We have the equation of the locus as t varies given by at P;
(2at)2=4a(at2)
Using h and k ,we can make the following substitutions;
(2×k)2=4a(h−a)
⇒4k2=4ah−4a2
Rewrite as ;
k2=ah−a2
⇒k2−ah+a2=0
Writing it in terms of x and y as;
y2−ax+a2=0 which is the standard locus at midpoint AP.
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