Răspuns:
Explicație pas cu pas:
sinx = [tex]\sqrt{1-cos^{2}x} =\sqrt{1-\frac{16}{25} } = \sqrt{\frac{25-16}{25} }=\sqrt{\frac{9}{25} } =\frac{3}{5}[/tex]
cos(x+π/6) = cosx*cos(π/6) -sinx*sin(π/6)= [tex]\frac{-4}{5}*\frac{\sqrt{3} }{2} - \frac{3}{5} *\frac{1}{2}=\frac{-4\sqrt{3} }{10} -\frac{3}{10}= \frac{-4\sqrt{3}-3}{10}[/tex]
