已知e1,e2,是夹角为60°的两个单位向量,设向量a=2*e1+e2,b=-3*e1+2*e2,求a与b的夹角

e1*e2=/e1//e2/cos60°=0.5
a1*a2=(2*e1+e2)(-3*e1+2*e2)
=-6e1^2+e1*e2+2e2^2
=-6+0.5+2=-3.5
/a/^2=a^2 ==(2*e1+e2)=(2*e1+e2)
/b/^2=b^2 )=(-3*e1+2*e2)(-3*e1+2*e2)
a*b=/a/*/b/*cosa
cosa=a*b/ (/a/*/b/)
a与b的夹角a=arccos[a*b/ (/a/*/b/)]
具体自己算一下