At what point on the circle x2 + y2 – 2x – 4y + 1 = 0, the tangent is parallel to x – axis.
Given:
The curve is x2 + y2 – 2x – 4y + 1 = 0
Differentiating the above w.r.t x
⇒ x2 + y2 – 2x – 4y + 1 = 0
⇒ 2x2 – 1 + 2y2 – 1 – 2 – 4
+ 0 = 0
⇒ 2x + 2y – 2 – 4
= 0
⇒ (2y – 4) = – 2x + 2
⇒
...(1)
= The Slope of the tangent = tan
Since, the tangent is parallel to x – axis
i.e,
⇒ = tan(0) = 0 ...(2)
tan(0) = 0
From (1) & (2),we get,
⇒ = 0
⇒ – (x – 1) = 0
⇒ x = 1
Substituting x = 1 in x2 + y2 – 2x – 4y + 1 = 0,we get,
⇒ 12 + y2 – 21 – 4y + 1 = 0
⇒ 1 – y2 – 2 – 4y + 1 = 0
⇒ y2 – 4y = 0
⇒ y(y – 4) = 0
⇒ y = 0 & y = 4
Thus, the required point is (1,0) & (1,4)