Posted by Matt on Saturday, March 23, 2013 at 11:13pm.
write an equation which must be true if the line from p(x,y) to a(25,0) is perpendicular to the line from P(x,y) to the center of the circle x^2+y^2=400

Math  Reiny, Sunday, March 24, 2013 at 1:01am
I will make the assumption that P is on the circle
then if the centre is the origin , called O
then slope PO = 1/slope PA
y/x = 1/(y/(x25) )
y/x = (25x)/y
y^2 = 25x  x^2
but y^2 = 400  x^2
400x^2 = 25x  x^2
25x = 400
x = 16