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Find the angle of intersection of the curves y2 = 4ax and x2 = 4by. - Mathematics

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Question

Find the angle of intersection of the curves y2 = 4ax and x2 = 4by.

Sum
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Solution

Given that y2 = 4ax  .....(i) and x2 = 4by  .....(ii)

Solving (i) and (ii), we get

`(x^2/(4"b"))^2` = 4ax

⇒ x4 = 64 ab2x

or x(x3 – 64 ab2) = 0

⇒ x = 0, x = `4"a"^(1/3) "b"^(2/3)`

Therefore, the points of intersection are (0, 0) and `(4"a"^(1/3) "b"^(2/3), 4"a"^(2/3)"b"^(1/3))`.

Again, y2 = 4ax

⇒ `"dy"/"dx" = (4"a")/"dx" = (2"a")/y` and x2 = 4by

⇒ `"dy"/"dx" = (2x)/(4"b") = x/(2"b")`

Therefore, at (0, 0) the tangent to the curve y2 = 4ax is parallel to y-axis and tangent to the curve x2 = 4by is parallel to x-axis.

⇒  Angle between curves = `pi/2`

At `(4"a"^(1/3)"b"^(2/3), 4"a"^(2/3)"b"^(1/3))`, m1  ......(Slope of the tangent to the curve (i))

= `2("a"/"b")^(1/3)`

= `(2"a")/(4"a"^(2/3)"b"^(1/3))`

= `1/2("a"/"b")^(1/3)`, m2  ....(Slope of the tangent to the curve (ii))

= `(4"a"^(1/3)"b"^(2/3))/(2"b")`

= `2("a"/"b")^(1/3)`

Therefore, tan θ = `|("m"_2 - "m"_3)/(1 + "m"_1 "m"_2)|`

= `|(2("a"/"b")^(1/3) - 1/2("a"/"b")^(1/3))/(1 + 2("a"/"b")^(1/3)  1/2("a"/"b")^(1/3))|`

= `(3"a"^(1/3) . "b"^(1/3))/(2("a"^(2/3) + "b"^(2/3))`

Hence, θ = `tan^-1((3"a"^(1/3) . "b"^(1/3))/(2("a"^(2/3) + "b"^(2/3))))`

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Chapter 6: Application Of Derivatives - Solved Examples [Page 126]

APPEARS IN

NCERT Exemplar Mathematics [English] Class 12
Chapter 6 Application Of Derivatives
Solved Examples | Q 13 | Page 126

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