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Resposta:

[tex]a) \frac{ \sqrt{3} }{2} \\ \\ b) \frac{ \sqrt{2} }{2} \\ \\ c) \frac{1}{2} \\ \\ d)1 \\ \\ e) \frac{1}{2} [/tex]

Explicação passo-a-passo:

Considere π=180°:

[tex]a) \: sen \frac{2\pi}{3} = sen \frac{2.180}{3} = sen \: 120° = sen60° = \frac{ \sqrt{3} }{2} [/tex]

[tex] b)cos \frac{5.180}{4} = cos \: 225° = cos \: 225 - 180 = cos \: 45° = \frac{ \sqrt{2} }{2} [/tex]

[tex]c) \: cos \frac{7.180}{2} = cos420° = cos420 - 360 = cos60° = \frac{1}{2} [/tex]

[tex]d)cos \: 6.180 = cos1080° = 1[/tex]

[tex]e)sen \frac{5.180}{6} = sen 150 ° = sen180 - 150 = sen30° = \frac{1}{2} [/tex]