Solve for sin a/2 when cos a=4/5 , o

Question

Solve for sin a/2 when cos a=4/5 , o<a<pi/2

dtan5457 · Answer

just to check, i got $$\frac{ 3\sqrt{10} }{ 10 }$$

correct?

dtan5457 · Answer

@Hoslos @Michele_Laino @mathstudent55

dtan5457 · Answer

oh crap why is this in chemistry...

anonymous · Answer

Right, using the calculator to first find a, you do :$$a=\cos^{-1} 4/5=36.9$$
Then do$$\sin (36.9/2)=0.316$$

anonymous · Answer

Somewhat your final answer is triple of mine. What did you do? @dtan5457

dtan5457 · Answer

$$\sqrt{\frac{ 1+\frac{ 4 }{ 5 } }{ 2 }}=\sqrt{\frac{ 9 }{ 10 }}=\frac{ 3\sqrt{10} }{ 10 }$$

anonymous · Answer

Why 1 + 4/5?

dtan5457 · Answer

attachment

dtan5457 · Answer

quadrant 1, positive, cos a=4/5

1+4/5

dtan5457 · Answer

@Hoslos

anonymous · Answer

Ok. I am not sure about that identity, but more simply, you should first find ''a'' given in the formula cos a=4/5. Then plot this a in the formula of sin given by sin a/2.

anonymous · Answer

Or directly like this:$$\sin (\frac{ \cos^{-1} (\frac{ 4 }{ 5} )}{ 2 })$$

dtan5457 · Answer

our answer is suppose to be the "exact answer" and have radicals, not be in complete decimal form