Đề kiểm tra Giữa kì 2 Toán 11 có đáp án (Mới nhất) (Đề 21)

A. $\stackrel{\to }{DM}=\frac{1}{2}\left(\stackrel{\to }{a}+\stackrel{\to }{c}-2\stackrel{\to }{b}\right)$

B.. $\stackrel{\to }{DM}=\frac{1}{2}\left(\stackrel{\to }{b}+\stackrel{\to }{c}-2\stackrel{\to }{a}\right)$

C. $\stackrel{\to }{DM}=\frac{1}{2}\left(\stackrel{\to }{a}+\stackrel{\to }{b}-2\stackrel{\to }{c}\right)$

D. $\stackrel{\to }{DM}=\frac{1}{2}\left(\stackrel{\to }{a}+\stackrel{\to }{b}-\stackrel{\to }{c}\right)$

A. $30°$

B. 45 $°$

C. 60 $°$

D. 90 $°$

A. m=1

B. m=-2

C. m= -1

D.m= 0