Respuesta :

To find

[tex]\cos 225^o[/tex]

Now,

[tex]\begin{gathered} \cos 225^o=\cos (180^o+45^o)^{} \\ =\cos (2\times90^o+45^o) \\ =-\cos 45^o \\ =-\frac{1}{\sqrt[]{2}} \end{gathered}[/tex]

So, the required value is

[tex]-\frac{1}{\sqrt[]{2}}[/tex]

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