b) cm cái j z pn

a)Ta có AO=DO(gt), BO=CO(gt)

AD và BC cắt nhau tại trung điểm mỗi đường

=> ABCD là hcn

Hình pn tự vẽ nha

Gọi E là trung điểm AH

\(\Rightarrow\) ME là đường trung bình của \(\Delta AHB\)

\(\Rightarrow ME//AB\) hay \(ME//NC\left(N\in CD\right)\) và \(ME=\dfrac{1}{2}AB\) (1)

\(\Rightarrow ME\perp BC\)

Ta có ME=1/2 AB

Mà AB=CD(cạnh đối của hình chữ nhật)

Và N là trung điểm của CD

\(\Rightarrow ME=NC\)(2)

Từ (1), (2)\(\Rightarrow MECN\) là hình bình hành \(\Rightarrow EC//MN\) (3)

Xét tam giác MBC có \(ME\perp BC\left(cmt\right);BH\perp AC\left(gt\right)\)

\(\Rightarrow CE\perp BM\)(3 đường cao giao nhau)(4)

Từ (3); (4) \(\Rightarrow BM\perp MN\)

Today, as with other days, I, along with my master, went out to plow the land, preparing for a good harvest. My job is very hard, but I do not complain because my boss treated me very well, fed me and built me ​​a stable cage. Pulling the plow, I saw a huge tiger crawling in the bushes of the other side of the road, not knowing what he was looking at but very attentive. I also give, without fear of the boss here, the big tiger, how strong, can not do anything to me.

When I finished plowing, I stood on the edge of the break and savored the fine grass, when the tiger appeared, he looked at me with curiosity and said, "Buffalo, I'm asking you this, big brother , why are you so healthy for a little man to send you? " At that moment I suddenly burst into laughter, I saw him as a jungle lord of the jungle, also out of the human life he is a foolish tiger. I do not want to explain much because I do not understand him so I told the tiger "Because people have intelligence."

Cho nhiều muối vào nước

Tính:  c )   9 13 : 3 26 - 8 13

Điền dấu <; >; = vào chỗ trống:

2....2 + 3     5....5 + 0     2 + 3....4 + 0

5....2 + 1     0 + 3 ...4     1 + 0....0 + 1

x³+27+(x+3)(x-9)=0

\(x^3+3^3+\left(x+3\right)\cdot\left(x-9\right)=0\)

\(\left(x+3\right)\left(x^2-3x+9\right)+\left(x+3\right)\left(x-9\right)=0\)

\(\left(x+3\right)\left(x^2-3x+9+x-9\right)=0\)

\(\left(x+3\right)\cdot\left(x^2-2x\right)=0\)

\(x\cdot\left(x+3\right)\cdot\left(x-2\right)=0\)

\(\left\{{}\begin{matrix}x=0\\x+3=0\\x-2=0\end{matrix}\right.\Rightarrow\left\{{}\begin{matrix}x=0\\x=-3\\x=2\end{matrix}\right.\)

Kết quả:  l i m n + 16 - n

A. 0

B. 10

C. 10

D. +∞