向量a,b 若|a|=1,|b|=1,cos<a,b>=2π/3,则a·(a-b)的值为?cos<a,a...答:向量b=(p,q),|a|=1,|b|=1,|a|=√(m^2+n^2)=1,m^2+n^2=1,|b|=√(p^2+q^2)=1,p^2+q^2=1,cos(2π/3)=(mp+nq)/(1*1)=mp+nq,mp+nq=-1/2,向量a-b=(m-p,n-q),a·(a-b)=m^2-pm+n^2-nq =(m^2+n^2)-(pm+nq)=1-(-1/2)=3/2.设向量a...