由a*b=丨a丨丨b丨cosα=2,得2*2* cosα=2,cosα=1/2,故α=π/3.即向量a,b的夹角为π/3.建立直角坐标系,不妨设a=(2,0),b=(1,√3),设c=(x,y),（a-c）*（b-2c）=0,代入得2x^2-5x+2+2y^2-√3y=0可化为(x-5/4)^2+(y-√3/4...