Answer:
Step-by-step explanation:
1+cos 2a=2cos^2a
cos a=√[(1+cos 2a)/2]
[tex]put~a=\frac{\pi }{8} \\2a=\frac{\pi }{4} \\\\cos\frac{\pi }{8} =\sqrt{\frac{1+cos \frac{\pi }{4} }{2} } \\=\sqrt{\frac{1+\frac{\sqrt{2}}{2} }{2} }\\=\frac{\sqrt{2+\sqrt{2}}}{2}[/tex]
