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)


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