Răspuns :
[tex]\it cosB=0,125;\ \ \ cosC=0,75\\ \\ \\ cos2C=2cos^2C-1=2\cdot0,5625-1=1,125-1=0,125=cosB\\ \\ cos2C=cosB\ \Longrightarrow 2C=B \Longrightarrow B=2C[/tex]
[tex]\it cosB=0,125;\ \ \ cosC=0,75\\ \\ \\ cos2C=2cos^2C-1=2\cdot0,5625-1=1,125-1=0,125=cosB\\ \\ cos2C=cosB\ \Longrightarrow 2C=B \Longrightarrow B=2C[/tex]