+0  
 
0
65
3
avatar+237 

cos(−θ)=√3/4 ,  sinθ < 0

What is the value of sinθ ?

 

A ) √13 / 4

 

B) √13 / 16

 

C) − √13 / 4

 

D) −√13 / 16

 

I think its C  but im not sure I feel like I am way off

jjennylove  Nov 17, 2018
 #1
avatar+92785 
+2

Note    cos (-θ)   =  cos(θ)

 

So

 

cos(θ)  = √3/4  =  x / r

And

sin (θ)  =  y / r

 

We need to find "y"  ....since  r is always positive  and the sine < 0....then y  must be negative

 

So

 

y   =  -sqrt  ( r^2  - x^2) =  - sqrt ( 4^2 - (sqrt(3) )^2 )  =  - sqrt ( 16 - 3)  =  -sqrt (13)

 

So.....

 

sin (θ)  =  - √13  / 4    ⇒   C 

 

 

 

cool cool cool

CPhill  Nov 17, 2018
 #2
avatar+237 
+1

 While you were composing the answer I used your explanation from the question before and it helped me be more certain on C and now with the explanation above it is clear it is C . smiley Thank You

jjennylove  Nov 17, 2018
 #3
avatar+92785 
+1

Glad to help  !!!

 

cool cool cool

CPhill  Nov 17, 2018

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