[latex] sin^270^o=cos^2(90^o-70^o)=cos^220^o[/latex] Expresia din enunț devine : [latex]it sin^2 20^o+cos^220^o =1 (A)[/latex]

sin²20+sin²70=1 sin²(90-70)+sin²70=1 (sin90*cos70+cos90*sin70)²+sin²70=1 |_1*cos 70_|+|_____0___| cos²70+sin²70=1-adevarat