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How to find cos theta?

Guest Mar 4, 2018
 #1
avatar+12560 
+1

You'll just have to use a calculator   to find   cos (-3/2 degrees) = .999657

 

 

or if you need   cos ( -3/2 radians) = .070737

ElectricPavlov  Mar 4, 2018
 #3
avatar+92805 
0

You got in a mess with this one EP   wink

But considering how may questions you answer correctly I do not think you need to be upset by a silly error here and there. :)

Melody  Mar 4, 2018
 #2
avatar+92805 
+1

\(tan \theta = -\frac{3}{2}\\ \)

---

Think about   \(tan \theta = +\frac{3}{2} \)    first

Draw a right angled triangle.

Mark an acute angle as theta.

opp = 3

adj=2

so hypotenuse  =     \(\sqrt{9+4}=\sqrt{13} \)

 

So for this triangle   \(cos\theta= \frac{2}{\sqrt{13}}=\frac{2\sqrt{13}}{13}\)

----

 

Now, tan is negative in the 2nd and 4th quadrant

In the 2nd quad Cos is negative and in the 4th quad Cos is positive.

So

 

\(cos\theta=\pm\frac{2\sqrt{13}}{13}\)

Melody  Mar 4, 2018

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