Answers>Maths>IB>Article

What is the limit for this function as x approaches 0? y(x)=(cos x)^(1/sin x)

When we try to simply compute y(0) we get 1 to infinity, which is indeterminate (we means we can either get 0, 1, infinity or God knows what else!). The way we want to approach these types of exercises is to play with the functions in order to create a fraction, so we can apply L'Hopital's Rule to the new limit! (a very useful rule which I can easily prove if the reader requires me to do so)By taking a step back, we notice that y(x) can be written as: f(x)^(1/g(x)), where f(x)=cos x and g(x)=sin x. (The reason I make this notation is simple. This trick is a very common one and it is useful for students to recognize it early on)Now we are going to use the wonders of natural logarithms! f(x)^(1/g(x)) is the same thing as e^[ln(f(x))/g(x)]. So our new mission is to find the limit of the exponential, which is now a fraction! By applying L'Hopital's Rule we get:Limit as x approaches 0 of ln(cos x)/sin x is equal to ...BE VERY CAREFUL WHEN APPLYING THE CHAIN RULE!!! :)... the limit as x approaches 0 of (1/cos x) * (-sin x) / cos x which is 0.Thus our initial limit is simply e to the power of 0, which gives us 1.

Answered by Maths tutor

1600 Views

See similar Maths IB tutors

Related Maths IB answers

All answers ▸

How to find the derivative of sqrt(x) from first principles?


Talk about the relation between differentiability and continuity on a real function and its derivative.


The sum of the first and third term of a geometric sequence is 72. The sum to infinity of this sequence is 360, find the possible values of the common ratio, r.


Consider the arithmetic sequence 5,7,9,11, …. Derive a formula for (i) the nth term and (ii) the sum to n terms. (iii) Hence find the sum of the first 20 terms.


We're here to help

contact us iconContact ustelephone icon+44 (0) 203 773 6020
Facebook logoInstagram logoLinkedIn logo

MyTutor is part of the IXL family of brands:

© 2025 by IXL Learning