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Tamil Nadu Board of Secondary EducationHSC Science Class 12

Show that the two curves x2 – y2 = r2 and xy = c2 where c, r are constants, cut orthogonally

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Question

Show that the two curves x2 – y2 = r2 and xy = c2 where c, r are constants, cut orthogonally

Sum
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Solution

Given curves x2 – y2 = r2  ......(1)

xy = c2   .......(2)

 Let (x1, y1) be the point of intersection of the given curves.

(1) ⇒ x2 – y2 = r2

Differentiating w.r.t ‘x’

`2x - 2y  ("d"x)/("d"y)` = 0

`("d"x)/("d"y) = x/y`

Now `(("d"x)/("d"y))_(((x_1, y_1)))` = m1

= `x_1/y_1`

(2) ⇒ xy = c2

Differentiating w.r.t ‘x’

`x ("d"y)/("d"x) + y*1` = 0

`("d"y)/("d"x) = - y/x`

 `(("d"x)/("d"y))_(((x_1, y_1)))` = m2

= `- y_1/x_1`

Now, `"m"_1 xx "m"_2 = x_1/y_1  xx (- y_1/x_1) = - 1`

Hence, the given curves cut orthogonally.

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Chapter 7: Applications of Differential Calculus - Exercise 7.2 [Page 15]

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Samacheer Kalvi Mathematics - Volume 1 and 2 [English] Class 12 TN Board
Chapter 7 Applications of Differential Calculus
Exercise 7.2 | Q 10 | Page 15

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