mn ơi giúp em với ạ
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a: Xét ΔBAC có
D là trung điểm của AB
M là trung điểm của AC
Do đó: DM là đường trung bình của ΔABC
Suy ra: DM//BC và \(DM=\dfrac{BC}{2}=3.5\left(cm\right)\)
Bài 4:
a: \(A=\left(x-5\right)\left(2x+3\right)-2x\left(x-3\right)+x+7\)
\(=2x^2+3x-10x-15-2x^2+6x+x+7\)
=-8
Bài 5:
a: \(x\left(x-1\right)-x^2+4x=-3\)
\(\Leftrightarrow x^2-x-x^2+4x=-3\)
hay x=-1
i: \(x^2-9x+8=0\)
\(\Leftrightarrow\left(x-1\right)\left(x-8\right)=0\)
\(\Leftrightarrow\left[{}\begin{matrix}x=1\\x=8\end{matrix}\right.\)
1.Yes, they do
2..Yes, it is
3.People buy fruits and flowers from the market and decorate their house
4.People visit their family and friends
a) She was taught how to write (by him).
b) The meeting has been cancelled (by them).
c) He is being interviewed by the manager at the moment.
d) The flowers should be kept in a warm place (by you).
e) This computer is made in the USA (by them).
f) When will he be told the news (by you)?
h) Is he going to be fired (by them)?
i) Have they been invited (by him), too?
k) When will the letters be sent by you?