[tex]\it sin^2x+cos^2x=1\ \ formula\ \ fundamental\breve a\ \ a\ \ trigonometriei\\ \\ Prin\ \ urmare:\ \ sin^230^o+cos^230^o=1\\ \\ tgx\cdot ctgx=tgx\cdot\dfrac{1}{tgx}=1\\ \\ Prin\ \ urmare:\ \ \ tg30^o\cdot ctg30^o=1\\ \\ \\ Analog,\ \ celelalte.[/tex]
