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Calculati sin2x,stiind ca cosx=4/5 ,x apartine {3pi/2 ,2pi}


Răspuns :

[tex]\sin x=-\sqrt{1-\cos^2x}=-\sqrt{1-\frac{16}{25}}=-\frac{3}{5}\\ \text{Obs: se ia cu "-" deoarece sinusul e negativ in cadranu IV} \\ \sin 2x=2\sin x\cos x=-2\frac{3}{5}\frac{4}{5}=-\frac{24}{25}[/tex]