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express each value as a trigonometric function of an angle in Quadrant I??

1. sin 390

2. sec(-1290)

thank you !!!!!

 May 17, 2018
 #1
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It is always the acute angle from the x axis that counts.

 

so you either use 180 or 360

 

1. sin 390 

one complete revolution and 30 degrees more. That is just   sin 30

 

 

2. sec(-1290)

 

1390/360 = 139/36 = 3 clockwise revolutions -210

-210 is equivalent to  360-210 = 150 which is in the second quad

180-150=30

sec = 1/cos and cos is negative in the second quad so so is sec

 

sec(-1290)= - sec(30)

 May 17, 2018

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