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HeroicZach's avatar

Why do I keep getting stuck when taking the derivative of the inverse cosecant function?

Asked by HeroicZach (195points) October 30th, 2009
7 responses
“Great Question” (0points)

Hello all,

So I’m attempting to directly prove that the derivative of the inverse cosecant: (d/dx) csc^-1(x) = -1 / [abs(x) sqrt(x^2 – 1)]

To get started, I swap x and y in the cosecant function expression y = csc^-1(x), and get:

x = csc(y)

Then I go ahead and take the derivative of that expression, and I get:

1 = -csc(y)cot(y) y’

So,

y’ = – 1 / [csc(y)cot(y)]

How do I change csc(y)cot(y) to the required abs(x) sqrt(x^2 -1)? Is this some bizarre trigonometric/Pythagorean identity of which I am not aware?

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Answers

Beta_Orionis's avatar

cosecant understand

ItalianPrincess1217's avatar

Wow. I feel much more stupid after reading this question than I did before I clicked on it.

faye's avatar

no kidding

Psychedelic_Zebra's avatar

@ItalianPrincess1217 yeah, I feel as dumb as a box of hair right now.

HeroicZach's avatar

@virtualist Thanks for the really helpful link.

@ItalianPrincess1217 @faye @Psychedelic_Zebra – Calculus is a magical study of awesome – you should really take a look sometime. It appears far more involved and intricate than it really is – memorize a few short and basic techniques and you can solve anything.

ccrow's avatar

@HeroicZach I think it would make my brain hurt

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