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If the curve ay + x2 = 7 and x3 = y, cut orthogonally at (1, 1), then the value of a is ______. - Mathematics

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Question

If the curve ay + x2 = 7 and x3 = y, cut orthogonally at (1, 1), then the value of a is ______.

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  • 1

  • 0

  • – 6

  • 6

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Solution

If the curve ay + x2 = 7 and x3 = y, cut orthogonally at (1, 1), then the value of a is 6.

Explanation:

Equation of the given curves are ay + x2 = 7  .....(i)

And x3 = y  .....(ii)

Differentiating eq. (i) w.r.t. x, we have

`"a" "dy"/"dx" + 2x` = 0

⇒ `"dy"/"dx" = - (2x)/"a"`

∴ m1 = `- (2x)/"a"` ......`("m"_1 = "dy"/"dx")`

Now differentiating eq. (ii) w.r.t. x, we get

3x2 = `"dy"/"dx"`

⇒ m2 = `3x^2`  .....`("m"_2 = "dy"/"dx")`

The two curves are said to be orthogonal if the angle between the tangents at the point of intersection is 90°.

∴ m1 × m2 = – 1

⇒ `(-2x)/"a" xx 3x^2` = – 1

⇒ `(-6x^3)/"a"` = – 1

⇒ 6x3 = a

(1, 1) is the point of intersection of two curves.

∴ 6(1)3 = a

So a = 6

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Chapter 6: Application Of Derivatives - Exercise [Page 139]

APPEARS IN

NCERT Exemplar Mathematics [English] Class 12
Chapter 6 Application Of Derivatives
Exercise | Q 39 | Page 139

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