Would someone mind explaining to me why I got this question wrong? Thank you so much for your help!

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2 Answers
Jun 23, 2018

55

Explanation:

using the half angle identity for cos

xcos(θ2)=±1+cosθ2

given π<θ<3π2 then

π2<θ2<3π4second quadrant

where cos(θ2)<0

cos(θ2)=1352

×××=15

×××=15×55=55

Jun 23, 2018

See explanation.

Explanation:

Think about it logically. π<θ<3π2, so θ lies in the 3rd quadrant. To get to the 3rd quadrant, you take the basic acute angle and add π or 180 to it. If you halve an angle between π and 3π2, it will always be greater than π2 because the original angle was greater than π to begin with. Now, realize that since θ2 is in the 2nd quadrant, cos(θ2) will always be negative because cosθ is negative in the 2nd and 3rd quadrant. This is why the correct answer should be 55.