3 years ago

The exact vaule of cos(247.5 degrees)

1 answer:

8 0

$cos(247.5 deg)=cos( \frac{495deg}{2})
 = - \sqrt{ \frac{1+cos(495deg)}{2} } 
 = -\sqrt{ \frac{1- \frac{ \sqrt{2} }{2} }{2} } 
 = \frac{ \sqrt{2- \sqrt{2} } }{2}$

You might be interested in

How solve this <br> x+y=5<br> X-y=7

Misha Larkins [42]

$elimination\ methode\\\\\underline{+\left\{\begin{array}{ccc}x+y=5\\x-y=7\end{array}\right}\ \ \ \ |add\ both\ sides\ of\ the\ equations\\.\ \ \ \ \ \ 2x=12\ \ \ \ \ |divide\ both\ sides\ by\ 2\\.\ \ \ \ \ \ \ \boxed{x=6}\\\\subtitute\ the\ value\ of\ x\ to\ the\ first\ equation:\\\\6+y=5\ \ \ \ |subtract\ 6\ from\ both\ sides\\\boxed{y=-1}\\\\Answer:\boxed{\left\{\begin{array}{ccc}x=6\\y=-1\end{array}\right}$