1) Aratati ca [tex] sin^{2}* \frac{\pi }{8} +sin^{2} *\frac{3\pi }{8} =1[/tex]
2) Stiind ca cos2x=2/3, iar x∈(0, π/2), calculati sin x si cos x.
3) Stiind ca sinx=3/5; x∈(π/2, π), calculati cosx, apoi sin x/2 si cos x/2.