Find the point on the curve at which the tangents are parallel to y – axis
Since the tangent is parallel to y–axis, its slope is not defined, then the normal is parallel to x–axis whose The Slope is zero.
i.e., = 0
⇒ = 0
⇒ = 0
⇒ y = 0
Substituting y = 0 in = 1,
= 1
⇒ x2 = 9
⇒ x = ±3
Thus, the required point is (3,0) & ( – 3,0)