folosim teorema cosinusului
cosB=(AB^2+BC^2-AC^2)/(2*AB*BC)
cosB=(8^2+6^2-7^2)/(2*8*6)
cosB=(64+36-49)/96
cosB=51/96
cosB=17/32
cosC=(AC^2+CB^2-AB^2)/(2*AC*CB)
cosC=(7^2+6^2-8^2)/(2*7*6)
cosC=(49+36-64)/84
cosC=21/84
cosC=1/4
cosB-cosC=[tex]\frac{17}{32}[/tex] - [tex]\frac{1}{4}[/tex]= [tex]\frac{17}{32}[/tex] - [tex]\frac{8}{32}[/tex] = [tex]\frac{9}{32}[/tex]
