1.若A,B,C能构成三角形,
则AB, AC, BC相互不平行
AB=6I-3J-3I+4J=3I+J
AC=3I-4J-(5-M)I+(3+M)J=(-2+M)I+(-1+M)J
BC=6I-3J-(5-M)I+(3+M)J=(1+M)I+MJ
即(-2+M)/3≠(-1+M)/1 解得M≠1/2
(1+M)/3≠M/1 解得M≠1/2
(1+M)/(-2+M)≠M/(-1+M) 解得M≠1/2
综上:实数M应满足M≠1/2
2. AB⊥AC
则3(-2+M)+1*(-1+M)=0
解得M=7/4
希望能帮到你,祝学习进步O(∩_∩)O