Cho A(0; 3), B(4; 0), C(–2; –5). Tính vecto AB, vecto BC
Cho A(0; 3), B(4; 0), C(–2; –5). Tính \(\overrightarrow {AB} \,\,.\,\,\overrightarrow {BC} \).
Lời giải
\[\overrightarrow {AB} = (4; - 3) = ({x_1};{x_2})\]
\[\overrightarrow {BC} = ( - 6; - 5) = ({y_1};{y_2})\]
\[ \Rightarrow \overrightarrow {AB} \,.\,\overrightarrow {BC} = {x_1}\,.\,{y_1} + {x_2}.{y_2} = 4\,.\,( - \,6) + ( - \,3)\,.\,( - \,5) = - \,9\].