SOLUTION: If cosθ=0.8 and 270<θ <360, find the exact value of sin2θ
a. -0.96
b. -0.6
c. 0.96
d. 0.28
Is it A?
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Question 198569: If cosθ=0.8 and 270<θ <360, find the exact value of sin2θ
a. -0.96
b. -0.6
c. 0.96
d. 0.28
Is it A?
Answer by jim_thompson5910(35256) (Show Source): You can put this solution on YOUR website!
Recall that +\cos^2(\theta)=1)
So if =0.8)
, then =0.8^2=0.64)
. Plug this into the identity above to get:
+0.64=1)
Now solve for )
:
=1-0.64=0.36)
=\sqrt{0.36}=0.6)
Now because 
, this means that the value of sine will be negative.
So this means that =-0.6)
Now recall the identity: =2\sin(\theta)\cos(\theta))
... Start with the given identity
=2(-0.6)(0.8))
... Plug in and
=-0.96)
... Multiply
So which means that the answer is A) -0.96. So you are correct. Good job.
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