31.
triunghiul este isoscel
ducem inaltimea AD perpendiculara pe BC
BD=DC=BC/2=6√3/2=3√3
cos B=BD/AB=3√3/6=√3/2
m(<B)=30⁰
32.
ducem inaltimea AD perpendiculara pe BC
notam BD=x
DC=15-x
AD²=10²-x²
AD²=(5√7)²-(15-x)²
10²-x² =(5√7)²-(15-x)²
100-x² =175-225+30x-x²
100+50 =30x
30x=150
x=5
AD=√(=10²-5²)=√(100-25)=√75=5√3
sin B=AD/AB=5√3/10=√3/2
m(<B)=60⁰
