Question

Answer 1

Bài 2 

a) \(\overrightarrow{AB}.\overrightarrow{CD}=AB.CD.cos180^o=-2.2=-4\)

b) \(\overrightarrow{AB}.\overrightarrow{NC}=AB.NC.cos\left(0^o\right)=a.\dfrac{a}{2}.1=\dfrac{a^2}{2}\)

c) \(\overrightarrow{AD}.\overrightarrow{NM}=AD.NM.cos\left(90^o+45^o\right)=a.\dfrac{a}{2}.\left(-sin45^o\right)=\dfrac{a^2}{2}.\dfrac{\sqrt{2}}{2}=\dfrac{a^2\sqrt{2}}{4}\)

d) \(\overrightarrow{BA}.\overrightarrow{MC}=BA.MC.cos90^o=0\)

Bài 4

a) \(\overrightarrow{AB}.\overrightarrow{AC}=AB.AC.cos60^o=4.4.\dfrac{1}{2}=8\)

b) \(\overrightarrow{AB}.\overrightarrow{BC}=AB.BC.cos120^o=4.4.\left(-\dfrac{1}{2}\right)=-8\)

c) \(\overrightarrow{AH}.\overrightarrow{BC}=AH.BC.cos90^o=0\)