Video Transcript
Find d by d๐ฅ of the inverse cot of ๐ฅ.
In this question, we need to find the derivative of the inverse of cot ๐ฅ with respect to ๐ฅ. We begin by letting ๐ฆ equal the inverse of cot ๐ฅ. Taking cot or the cotangent of both sides of this equation gives us cot ๐ฆ is equal to ๐ฅ. Our next step is to differentiate both sides of this equation with respect to ๐ฅ. We know that differentiating cot ๐ฅ with respect to ๐ฅ gives us negative cosec squared ๐ฅ.
Using our knowledge of implicit differentiation, differentiating cot ๐ฆ with respect to ๐ฅ gives us negative cosec squared ๐ฆ multiplied by d๐ฆ by d๐ฅ. Differentiating ๐ฅ on the right-hand side gives us one. We can then divide both sides of this equation by negative cosec squared ๐ฆ so that d๐ฆ by d๐ฅ is equal to negative one over cosec squared ๐ฆ. Whilst we do have an expression for d๐ฆ by d๐ฅ, this is not in terms of ๐ฅ.
Returning to the point where cot ๐ฆ was equal to ๐ฅ, weโll now square both sides of this equation. This gives us cot squared ๐ฆ is equal to ๐ฅ squared. One of our trigonometrical identity states that cot squared ๐ plus one is equal to cosec squared ๐. Rearranging this, we see that cot squared ๐ is equal to cosec squared ๐ minus one.
This means that cot squared ๐ฆ is equal to cosec squared ๐ฆ minus one. And we know this is equal to ๐ฅ squared. We can then add one to both sides of this equation so that cosec squared ๐ฆ is equal to one plus ๐ฅ squared. Finally, we substitute this into the denominator in our expression for d๐ฆ by d๐ฅ.
d๐ฆ by d๐ฅ is equal to negative one over one plus ๐ฅ squared. This is the derivative of the inverse cotangent function.