Răspuns:
[tex](sinx+cosx)^2+(sinx-cosx)^2=2[/tex]
[tex]sin^2x+cos^2x+2sinx*cosx+sin^2x+cos^2x-2sinx*cosx=2[/tex]
[tex]2(sin^2x+cos^2x)=2[/tex]
Dupa formula fundamentala a trigonometriei [tex]sin^2x+cos^2x=1[/tex]
[tex]=> 2*1=2[/tex] "Adevarat"