DA = BA - BD = BA - (BC + CD) = -a - (b + c) = - (a + b + c)
向量AB-向量AC
= AB - (AB + BC)
= - BC
= -b
向量AB-向量AE
=AB - (AD + DE)
= AB + DA - DE
= a -(a+b+c) - d
= -(b+c+d)
DA = BA - BD = BA - (BC + CD) = -a - (b + c) = - (a + b + c)
向量AB-向量AC
= AB - (AB + BC)
= - BC
= -b
向量AB-向量AE
=AB - (AD + DE)
= AB + DA - DE
= a -(a+b+c) - d
= -(b+c+d)