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Here's the question:

 

 Jun 10, 2018
 #1
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Remeber    cos^2 + sin^2 = 1

1 - sin^2 = cos^2

1 - 5/25 = cos^2

20/25 = cos^2       cos = +- 2sqrt(5)/5  

since it is in quadrant II  cos is negative    - 2 sqrt5/5

 Jun 10, 2018

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