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timurjin [86]
3 years ago
13

Find the value of sin(a/2) if cosa= 12/13​

Mathematics
1 answer:
daser333 [38]3 years ago
5 0

Answer: sin\frac{a}{2} = ± \frac{1}{\sqrt{26} }

Step-by-step explanation:

We very well know that,

cos2A=1−2sin²A

⟹ sinA = ±\sqrt{(1-} \frac{cos2A}{2} )

As required,  set A = \frac{a}{2}   &   cos a=  \frac{12}{13}    ,thus we get

sin \frac{a}{2} =± \sqrt{\frac{1-cos a}{2} }  

∴ sin\frac{a}{2} =±\sqrt{\frac{1-\frac{12}{13} }{2} } = ± \frac{1}{\sqrt{26} }

   since ,360° < \frac{a}{2} <450°

             ,180° < \frac{a}{2} <225°

Now, we are to select the value with the correct sign. It's is obvious from the above constraints that the angle a/2 lies in the III-quadrant where 'sine' has negative value, thus the required value is negative.

hope it helped!

   

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