Din teorema cosinului:
=>
[tex] AC^2=AB^2+ BC^2-2 AB* AC *cosB\\\\
\Longrightarrow~cosB= \frac{AB^2+BC^2-AC^2}{2AB*BC}=\frac{16+3-7}{2*4 \sqrt{3} }= \frac{12}{8 \sqrt{3}}= \frac{3}{2 \sqrt{2} } = \frac{3 \sqrt{3} }{2*3}= \frac{ \sqrt{3} }{2} \Longrightarrow\\\\
\Longrightarrow ~cosB=\frac{ \sqrt{3} }{2} \\\\
\Longrightarrow ~m (\ \textless \ B) = 30\°[/tex]
