Michael J. answered • 11/28/16
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Effective High School STEM Tutor & CUNY Math Peer Leader
Let x=θ
sinx = √(1 - cos2x)
sinx = √(1 - (-3/5)2)
sinx = √(1 - (9/25))
sinx = √(16 / 25)
sinx = 4/5
a)
sin(2x) = 1 - 2sin2x
b)
sin(2x) = 2sinxcosx
All you have to do is plug in the known values of sinx and cosx to answer parts a and b.
Michael J.
I think you missed the last statement when I said plug in the values of sinx and cosx into the identities. I will do the first one for you so you know how it is done.
cos(2x) = 1 - 2sin2x
= 1 - 2(16/25)
Simplify.
Now try the other one.
Report
11/30/16
Asia M.
So, for cos (2θ)= (-7/25). Now you have to use the equation sin(2x)=2sinxcosx and plug in both sinx and cosx to get (b) I believe. I would go about that by doing this: 2(4/5)(-7/25). Then you get -56/125 for sin(2θ). Am I Right?
Report
11/30/16
Asia M.
11/30/16