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TomyIby
a fost răspuns

Daca cosx = 5/13, aflati cos2x.

Răspuns :

Albatran
sinx=+-√(1-(5/12)²) =+-12/13
sin²x=144/169

cos2x=cos²x-sin²x=1-2sin²x=1-2(12/13)²=1-288/169=-119/169
[tex]sinx= \sqrt{1-( \frac{5}{13})^2 }= \frac{12}{13} \\ cos2x=cos^2x-sin^2x= \frac{25}{169}- \frac{144}{169}=- \frac{119}{169} [/tex]

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