14455
1 x 4 - 4 + 5 = 5
This is another one that I've just done, got the correct answer. Turning off music helps with maths apparently

Two points P(2ap, ap^2) and Q(2aq, aq^2) are on the parabola x^2 = 4ay.
The normal to P is given by x + py = 2ap + ap^3 and the normal to Q is given by x + qy = 2aq + aq^3.
The point R is the intersection of the normals to P and Q. Find R.
My working:
1) x = 2ap + ap^3 - py
2) x = 2aq + aq^3 - qy
2ap + ap^3 - py = 2aq + aq^3 - qy
2ap - 2aq + ap^3 - ap^q + qy - py = 0
2a(p - q) + a(p^3 - q^3) + y(q - p) = 0
2a(p - q) + a(p - q)(p^2 + 2pq + q^2) = y(p - q)
[Divide everything by (p - q)]
y = 2a + a(p^2 + 2pq + q^2)
y = a(p^2 + 2pq + q^2 + 2)
(y co-ordinate found)
1) y = 2a + ap^2 - x/p
2) y = 2a + aq^2 - x/q
2a + ap^2 - x/p = 2a + aq^2 - x/q
2ap + ap^3 - x = 2ap + aq^2p - xp/q
2apq + ap^3q - xq = 2apq + aq^3p - xp
2apq - 2apq + ap^3q - aq^3p - x(p - q) = 0
apq(q^2 - p^2) = -x(q - p)
apq(q - p)(q + p) = -x(q - p)
[Divide everything by (q - p)]
apq(p + q) = -x
x = -apq(p + q)
[x co-ordinate found]
Therefore R = [-apq(p + q), a(p^2 + 2pq + q^2 + 2)]
And that was correct
