Cho bốn điểm A,B,C,DA,B,C,D. Tìm các vec tơ:
a) \(\overrightarrow u = \overrightarrow {AB} + \overrightarrow {DC} + \overrightarrow {BD} + \overrightarrow {CA} \)
b) \(\overrightarrow v = \overrightarrow {AB} + \overrightarrow {CD} + \overrightarrow {BC} + \overrightarrow {DA} \)
a) \(\overrightarrow u = \overrightarrow {AB} + \overrightarrow {DC} + \overrightarrow {BD} + \overrightarrow {CA} \)
\( = \left( {\overrightarrow {AB} + \overrightarrow {BD} } \right) + \left( {\overrightarrow {DC} + \overrightarrow {CA} } \right) = \overrightarrow {AD} + \overrightarrow {DA} = \overrightarrow {AA} = \overrightarrow 0 \)
b) \(\overrightarrow v = \overrightarrow {AB} + \overrightarrow {CD} + \overrightarrow {BC} + \overrightarrow {DA} \)
\( = \left( {\overrightarrow {AB} + \overrightarrow {BD} } \right) + \left( {\overrightarrow {DC} + \overrightarrow {CA} } \right) = \overrightarrow {AD} + \overrightarrow {DA} = \overrightarrow {AA} = \overrightarrow 0 \)
-- Mod Toán 10