Aplicam formula (a+b)^2 si avem:
Stiind ca: [tex]sin^{2} x + cos^{2} x = 1[/tex] si [tex]2sinx*cosx = sin2x[/tex]=>
[tex](sinx+cosx) ^{2} = sin^{2} x + 2sinx*cosx + cos^{2} x \\ 2sinx*cosx = (sinx+cosx) ^{2} - 1 \\ sin2x = (\frac{3}{5})^{2} -1 \\ sin2x = \frac{9}{25} - 1 \\ sin2x = \frac{9}{25} - \frac{25}{25}[/tex]
=> [tex]sin2x = - \frac{16}{25} [/tex]
