x,y [tex]x,y.apartinand.(0.pi/2)-\ \textgreater \ x,y.apartin.Cadranului.1.[/tex]
[tex]sin.x\ \textgreater \ 0 ,si.cosx\ \textgreater \ 0;sin.y\ \textgreater \ 0,si.cos.y\ \textgreater \ 0[/tex]
[tex]cos(x-y)=cosx·cosy+sinx·siny[/tex]
Se foloseste formula de calcul a functiilor trigonometrice a sumei si a diferentei intre unghiuri
sin²x+cos²x=1
sin²x=1-(1/7)²
sin²x=1-1/49
sinx=√48/49
sinx=4√3/7
sin²y+cos²y=1
sin²y=1-(13/14)²
sin²y=1-169/196
siny=√27/196
siny=3√3/13
cos(x-y)=1/7·13/14+4√3/7·3√3/14=13/98+36/98
cos(x-y)=49/98
cos(x-y)=1/2
