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महाराष्ट्र राज्य शिक्षण मंडळएचएससी विज्ञान (सामान्य) इयत्ता १२ वी

If x = θθθθthen show thatdydxasecθ-tanθ,y=asecθ+tanθ,then show thatdydx=-yx. - Mathematics and Statistics

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प्रश्न

If x = `asqrt(secθ - tanθ), y = asqrt(secθ + tanθ), "then show that" "dy"/"dx" = -y/x`.

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उत्तर

x = `asqrt(secθ - tanθ), y = asqrt(secθ + tanθ)`

∴ `x/a = sqrt(secθ - tanθ), y/a = sqrt(secθ + tanθ)`

∴ `sec θ - tanθ = x^2/a^2`   ...(1)

`sec θ + tanθ = y^2/a^2`  ...(2)
Adding (1) and (2), we get
2secθ = `x^2/a^2 + y^2/a^2`

= `(x^2 + y^2)/a^2`

∴ secθ = `(x^2 + y^2)/(2a^2)`
Subtracting (1) from (2), we get
2tanθ = `y^2/a^2 - x^2/a^2`

= `(y^2 - x^2)/a^2`

∴ tanθ  = `(y^2 - x^2)/(2a^2)`
∴ sec2θ - tan2θ = 1 gives,
`((x^2 + y^2)/(2a^2))^2 - ((y^2 - x^2)/(2a^2))^2` = 1
∴ (x2 + y2)2 - (y2 - x2)2 = 4a4
∴ (x4 + 2x2y2 + y4) - (y4 - 2x2y2 + x4) = 4a4
∴ 4x2y2 = 4a4
∴ x2y2 = a4
Differentiating both sides w.r.t. x, we get
`x^2."d"/"dx"(y^2) + y^2."d"/"dx"(x^2)` = 0

∴ `x^2 xx 2y"dy"/"dx" + y^2 xx 2x` = 0

∴ `2x^2y"dy"/"dx"` = -2xy2

∴ `"dy"/"dx" = -y/x`.

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पाठ 1: Differentiation - Exercise 1.4 [पृष्ठ ४८]

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