|a|²=(2e1+e2)²=4e1²+4e1*e2+e2²=4+4×1×1×cos60+1=7|b|²=(-3e1+2e2)²=9e1²-12e1*e2+4e2²=9-12×1×1×1/2+4=7a*b=(2e1+e2)(-3e1+2e2)=-6e1²+e1*e2+2e2²=-6+(1...