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What is the value of cos(−θ)cos(−θ) ?

 Mar 4, 2018
 #1
avatar+99659 
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sin (-theta)  =  - sin (theta)

 

So

 

-sin (theta)  = -3/5      multiply both sides by -1

 

sin (theta)  = 3/5

 

And  cos(-theta)  =  cos(theta)

 

So......  the sine , tan > 0        this must be a first quadrant angle

 

So....cos (theta)  =

 

√ [ 1  -  sin^2 (theta) ]  =    √ [ 1 - (3/5)^2 ]  =  √ [ 1 - 9/25]  =

 

√ [ 25 - 9 ]  / 5  =     √ 16 /  5      =  4/5

 

 

cool cool cool

 Mar 4, 2018

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