Question 333611
A) if 0 
What?
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B) if sin x= 0.2, find cos 2x
{{{cos(x) = sqrt(1 - sin^2(x)) = sqrt(1 - 0.04)}}}
{{{cos(x) = sqrt(0.96)}}}
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sin(2x) = 2sin(x)cos(x)
= {{{2*0.2*sqrt(0.96) = 0.4*sqrt(0.96)}}}
{{{cos(2x) = sqrt(1 - sin^2(2x)) = sqrt(1 - 0.16*0.96) = sqrt(0.8464)}}}
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