How do you use csctheta=5cscθ=5 to find cotthetacotθ?

2 Answers
Mar 27, 2017

cottheta=+-2sqrt6cotθ=±26

Explanation:

The terminal ray of an angle thetaθ in standard position intersects a point (x,y)(x,y) on the unit circle such that csctheta=1/ycscθ=1y, cottheta=x/ycotθ=xy, and x^2+y^2=1x2+y2=1.

Knowing that csctheta=5cscθ=5 we know that y=1/5y=15

Since x^2+y^2=1x2+y2=1, x=+-sqrt(1-y^2)x=±1y2

cottheta=x/y=(+-sqrt(1-y^2))/y=(+-sqrt(1-(1/5)^2))/(1/5)cotθ=xy=±1y2y=±1(15)215
cottheta=+-5sqrt(1-1/25)=+-5sqrt(24/25)=+-cancel5sqrt24/cancel5=+-2sqrt6

Mar 27, 2017

+- 2sqrt6

Explanation:

Use trig identity:
1 + cot^2 t = csc^2 t
In this case:
1 + cot^2 t = 25
cot^2 t = 24
cot t = +- 2sqrt6