Răspuns:
5. u= (m+1)i + 8j
v= (m-1)i - 4j - rel.vectoriale
u, v coliniari <=> m+1/m-1 = 8/-4
m+1/m-1 = -2 => m+1= -2*(m-1) <=> m+1 = -2m+2 <=> 3m=1 <=> m=1/3 ∈ R
6. AB=5 =c
BC=7=a
AC=8=b
Apl. t.cosinusului : cos A= b²+c²-a²/ 2bc
cosA= 8²+5²-7²/2*8*5
cosA= (8-7)(8+7) +5²/ 2*8*5
cosA= 1*15+25/2*8*5
cosA= 40/2*8*5
cosA=4/8=1/2 => m(∡A)=60°
