Let the point at which the normal on the curve x2 = 4y passes through the point (1, 2) be P(x1 ,y1)
Now x2 = 4y ......(i)
Since P(x1 , y1) lies on (i), so
x21 = 4y1 .....(ii)
Differentiate (i) w.r.t. to x both sides,
or x + y = 3
and the equation of tangent is :
y - 1 = 2/2(x - 2)
or y - 1 = x - 2
or x - y = 1