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Prove that the curves xy = 4 and x2 + y2 = 8 touch each other. - Mathematics

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प्रश्न

Prove that the curves xy = 4 and x2 + y2 = 8 touch each other.

योग
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उत्तर

Given circles are xy = 4   .....(i)

And x2 + y2 = 8   .....(ii)

Differentiating equation (i) w.r.t., x

`x * "dy"/"dx" + y * 1` = 0

⇒ `"dy"/"dx" = - y/x`

⇒ m1 = `- y/x`  .....(iii)

Where, m1 is the slope of the tangent to the curve.

Differentiating equation (ii) w.r.t. x

`2x + 2y * "dy"/"dx"` = 0

⇒ `"dy"/"dx" = - x/y`

⇒ m2 = `- x/y`

Where, m2 is the slope of the tangent to the circle.

To find the point of contact of the two circles

m1 = m2

⇒ `- y/x = - x/y`

⇒  x2 = y2

Putting the value of y2 in equation (ii)

x2 + x2 = 8

⇒ 2x2 = 8

⇒ x2 = 4

∴ x = ± 2

∵ x2 = y2

⇒ y = ± 2

∴ The point of contact of the two circles are (2, 2) and (– 2, 2).

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अध्याय 6: Application Of Derivatives - Exercise [पृष्ठ १३६]

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एनसीईआरटी एक्झांप्लर Mathematics [English] Class 12
अध्याय 6 Application Of Derivatives
Exercise | Q 13 | पृष्ठ १३६

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