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If log5 yy(x4+y4x4-y4) = 2, show that dydydydx=12x313y2

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Question

If log5 `((x^4 + "y"^4)/(x^4 - "y"^4))` = 2, show that `("dy")/("d"x) = (12x^3)/(13"y"^2)`

Sum
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Solution

log5 `((x^4 + "y"^4)/(x^4 - "y"^4))` = 2

log5 `((x^4 + "y"^4)/(x^4 - "y"^4))` = 2 `"log"_5^5`     (∴ `"log"_5^5` = 1 )

∴ log5 `((x^4 + "y"^4)/(x^4 - "y"^4)) = "log"_5^(5^2)`

∴ `(x^4 + "y"^4)/(x^4 -"y"^4)` = 5         (∴ log a = log b ⇒ a = b)

∴ x4 +y4 = 25(x4 - y4)

∴ x4 + y4 = 25x4 – 25y4

∴ y4 + 25y4 = 25x4 - x4

∴ 26y4 = 24x4 

Differentiating w. r. t. x, we get

∴ `26xx4y^3("dy")/("d"x) = 24xx4x^3`

∴ `("dy")/("d"x) = (24xx4x^3)/(26xx4"y"^3)`

∴ `("dy")/("d"x) = (12x^3)/(13"y"^3)`

Hence proved.

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Chapter 2.1: Differentiation - Short Answers II

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