Solve the equation cosec^2(x) = 1 + 2cot(x), for -180° < x ≤ 180°.

First, we want to convert the equation to a simpler form involving just one function of x. Squared trigonometric functions are normally good candidates for simplification, thanks to the trigonometric identities. Using the identity:cot^2(x) + 1 = cosec^2(x),we see the left-hand side simplifies to:cot^2(x) + 1 = 1 + 2cot(x).Rearranging,cot^2(x) – 2cot(x) = 0.We now have a simple quadratic equation in terms of the single variable cot(x). Since there is no constant term, we can factorise the quadratic by taking out a factor of cot(x), leaving:cot(x)*(cot(x) – 2) = 0.By the factor theorem, the solutions are therefore:cot(x) = 0, and cot(x) = 2.We want solutions in the domain -180° < x ≤ 180°. Using that cot(x) = 1/tan(x), we write the above in terms of tan(x) as:tan(x) = ±∞, and tan(x) = 1/2,where we have noted that either a plus or minus infinite value of tan(x) gives cot(x) = 0. These are two different solutions to the equation, which we investigate separately to find all possible solutions in terms of x.1) tan(x) = ±∞: Referring to a graph of tan(x), for example the one at https://commons.wikimedia.org/wiki/File:Tan_proportional.svg, we can easily see the plus and minus infinities are at x = 90° and x = –90°. These are the only solutions in this domain.2) tan(x) = 1/2: The most obvious solution is to take x = arctan(1/2), which we find on a calculator as 26.6°. However looking back at our graph, there is another solution translated by –180°. This second solution is 26.6° – 180° = 153.4°. So, our final answer is x = ±90°, x = 26.6° and x = 153.4°.

Answered by Max H. Maths tutor

8622 Views

See similar Maths A Level tutors

Related Maths A Level answers

All answers ▸

In a triangle ABC, side AB=10 cm, side AC=5cm and the angle BAC=θ, measured in degrees. The area of triangle ABC is 15cm(sq). Find 2 possible values for cosθ and the exact length of BC, given that it is the longest side of the triangle.


How do you integrate ln(x)?


Express cos2x in the form a*cos^2(x) + b and hence show that the integral of cos^2(x) between 0 and pi/2 is equal to pi/a.


Find the integral of log|x| by integration by parts


We're here to help

contact us iconContact usWhatsapp logoMessage us on Whatsapptelephone icon+44 (0) 203 773 6020
Facebook logoInstagram logoLinkedIn logo

© MyTutorWeb Ltd 2013–2024

Terms & Conditions|Privacy Policy
Cookie Preferences