Question 997999
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*[tex \LARGE \ \ \ \ \ \ \ \ \ \ \cos(\alpha\ -\ \beta)\ =\ \cos\alpha\cos\beta\ +\ \sin\alpha\sin\beta]


If *[tex \LARGE \sin\varphi\ =\ a] then *[tex \LARGE \cos\varphi\ =\ \pm\sqrt{1\ -\ a^2}]


That's all I can do for you since I don't know whether you mean *[tex \Large \sin(s)\ =\ \sqrt{\frac{5}{7}}] or *[tex \Large \frac{sqrt{5}}{7}].


Either way, there will be two answers depending on the signs of *[tex \Large \cos(s)] and *[tex \Large \cos(t)]


John
*[tex \LARGE e^{i\pi}\ +\ 1\ =\ 0]
My calculator said it, I believe it, that settles it

*[tex \Large \ \
*[tex \LARGE \ \ \ \ \ \ \ \ \ \  

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