[V.Rattanapon]

ข้อ 3. \[
x = \cos \left( {\frac{\pi }{6} + \frac{2}{3}\arccos \frac{3}{5}} \right),\frac{{24}}{{25}}
\]

ข้อ 4. \[
\pm \left( {\frac{{\sqrt {5 - 4x} + \sqrt {2x - 3} }}{{\sqrt 2 }}} \right)
\]