SOLUTION: I am super confused with this type of questions. I would be grateful for your help. Thanks in advance. A) if 0<x<&#960; /2 and tan x = 15/8, cos 2x= B) if sin x= 0.2, find cos

Algebra ->  Trigonometry-basics -> SOLUTION: I am super confused with this type of questions. I would be grateful for your help. Thanks in advance. A) if 0<x<&#960; /2 and tan x = 15/8, cos 2x= B) if sin x= 0.2, find cos       Log On


   

Question 333611: I am super confused with this type of questions. I would be grateful for your help. Thanks in advance.
A) if 0 B) if sin x= 0.2, find cos 2x
C)find sin 7π /12; how to I get here: (1+√3)/2√2
D) use π /12=(π /3)-(π /4) to find cos π /12
THANK YOU!!!!!!!!!!
Answer by Alan3354(69443) About Me  (Show Source):
You can put this solution on YOUR website!
A) if 0
What?
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B) if sin x= 0.2, find cos 2x
cos%28x%29+=+sqrt%281+-+sin%5E2%28x%29%29+=+sqrt%281+-+0.04%29
cos%28x%29+=+sqrt%280.96%29
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sin(2x) = 2sin(x)cos(x)
= 2%2A0.2%2Asqrt%280.96%29+=+0.4%2Asqrt%280.96%29
cos%282x%29+=+sqrt%281+-+sin%5E2%282x%29%29+=+sqrt%281+-+0.16%2A0.96%29+=+sqrt%280.8464%29
cos(2x) = 0.92
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Repost the others, don't post several problems at one time. The tutors are much more likely to ignore them if you do.
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C)find sin 7π /12; how to I get here: (1+√3)/2√2
D) use π /12=(π /3)-(π /4) to find cos π /12