[tex]\boxed{\boxed{sin^2B+cos^2B=1}}-teorema~fundamentala~a~trigonometriei[/tex]
[tex]Demonstratie: \\ \\ sin^2B= (\frac{b}{a}) ^2= \frac{b^2}{a^2}. \\ \\ cos^2B= (\frac{c}{a})^2= \frac{c^2}{a^2} \\ \\ T.Pitagora: b^2+c^2=a^2. \\ \\ sin^2B+cos^2B= \frac{b^2}{a^2}+ \frac{c^2}{a^2}= \frac{b^2+c^2}{a^2}= \frac{a^2}{a^2}=1. [/tex]
