jika sudut antara vektor a = (2,1,-3) dan vektor b = (-1,3,-2) adalah a, besarnya a adalah.

vektor a=A vektor b=B                                            panjang A=√2²+1²+3²
                                                                                                =√4+1+9 = √14

                                                                                panjang B=√(-1²)+3²+(-2²)
                                                                                                 =√1+9+4 =√14

cos a = (A * B) /  (panjang A * Panjang B)
cos a = (2*(-1))+(1*3)+(-3*(-2)) / (√14*√14)
cos a =7 / 14
cos a  =¹/₂
sudut a = 60⁰

semoga membantu..