+0  
 
0
5876
3
avatar

Given cot \Theta=1/4, find sin \Theta and sec \Theta

 Oct 28, 2015

Best Answer 

 #1
avatar+6250 
+5

\(\cot(\theta)=\dfrac 1 4 \\ \dfrac {\cos(\theta)}{\sin(\theta)}=\dfrac 1 4 \\ \dfrac{\sqrt{1-\sin^2(\theta)}}{\sin(\theta)}=\dfrac 1 4\\ \dfrac{1-\sin^2(\theta)}{\sin^2(\theta)}=\dfrac 1 {16} \\ 16 -16\sin^2(\theta)=\sin^2(\theta)\)

\(16 = 17\sin^2(\theta) \\ \sin^2(\theta)=\dfrac {16}{17} \\ \sin(\theta)=\sqrt{\dfrac{16}{17}}=\dfrac{4}{\sqrt{17}}\)

\(\cos(\theta)=\sqrt{1-\sin^2(\theta)} = \sqrt{1-\left(\dfrac{4}{\sqrt{17}}\right)^2}=\sqrt{\dfrac {1}{17}}\\ \sec(\theta)=\dfrac 1 {\cos(\theta)} = \sqrt{17}\)

.
 Oct 28, 2015
 #1
avatar+6250 
+5
Best Answer

\(\cot(\theta)=\dfrac 1 4 \\ \dfrac {\cos(\theta)}{\sin(\theta)}=\dfrac 1 4 \\ \dfrac{\sqrt{1-\sin^2(\theta)}}{\sin(\theta)}=\dfrac 1 4\\ \dfrac{1-\sin^2(\theta)}{\sin^2(\theta)}=\dfrac 1 {16} \\ 16 -16\sin^2(\theta)=\sin^2(\theta)\)

\(16 = 17\sin^2(\theta) \\ \sin^2(\theta)=\dfrac {16}{17} \\ \sin(\theta)=\sqrt{\dfrac{16}{17}}=\dfrac{4}{\sqrt{17}}\)

\(\cos(\theta)=\sqrt{1-\sin^2(\theta)} = \sqrt{1-\left(\dfrac{4}{\sqrt{17}}\right)^2}=\sqrt{\dfrac {1}{17}}\\ \sec(\theta)=\dfrac 1 {\cos(\theta)} = \sqrt{17}\)

Rom Oct 28, 2015
 #2
avatar+118629 
+5

Thanks Rom,

 

When I do these i start by drawing a right anged triangle and mark one of the acute angels as theta.

sine cot theta = 1/4

opposite will be 4 and adjacent will be 1

use pythagoras to get the third side    sqrt(1+16) = sqrt{(17)

 

Now you can read all th other ratios off the triangle.

This only gives you the ratios for the acute angles though.

 

Since cot is positive, tan is positive so theta can be in the 1st OR third quadrants.

So some of the ratios can be + or - 

 

 

:))

 Oct 28, 2015
 #3
avatar
0

Given cot Theta = 40, what is sin theta and sec theta?

 Oct 3, 2016

1 Online Users

avatar