Kẻ phân giác AD, BK vuông góc với AD.

\(\sin\frac{\widehat{A}}{2}=\sin BAD\)

Xét tam giác AKB vuông tại K, ta có:

\(\sin BAD=\frac{BK}{AK}\left(1\right)\)

Xét tam giác BKD vuông tại K, ta có: 

\(BK\Leftarrow BD\)thay vào (1)

\(\sin BAD\Leftarrow\frac{BD}{AB}\left(2\right)\)

Lại có: \(\frac{BD}{CD}=\frac{AB}{AC}\)

\(\Rightarrow\frac{BD}{\left(BD+CD\right)}=\frac{AB}{\left(AB+AC\right)}\)

\(\Rightarrow\frac{BD}{BC}=\frac{AB}{\left(AB+AC\right)}\)

\(\Rightarrow BD=\frac{\left(AB.BC\right)}{\left(AB+AC\right)}\)thay vào (2)

\(\sin BAD\Leftarrow\frac{\left[\frac{\left(AB.BC\right)}{\left(AB+AC\right)}\right]}{AB}\)

\(=\frac{BC}{\left(AB+AC\right)}\left(ĐPCM\right)\)

234+567=801

Số cần tìm là :

234 + 567 = 801

Đáp số : 801

xe đó chở được số khối đá là

37,6 x 21,8 x 1,35=1106568(khối)

Đáp số 1106568 khối đá

My family is small . Thera are only four members in my family . They are my father , mymother , my sister and me .
My father is a teacher . He is about forty-five years old . My mother works at home . She is afew years younger than father . My sister goes to school . She is sixteen years old . I’m five yearsyoungers than my sister .
Everyone in my family is good and happy . My father and my mother love my sister and mevery much . They buy manything for us . Sometimes they takes us to the cinema . They also tell usmany interesting stories . Sometimes thay help us in our studies .
I need , I love my family very much .

 
We are a poor family . There are altogether nine members in my family , including my father andmy mother . The children are seven in all , four boys and three girls .
My father is a hawker selling fruits in the streets of Singapore and my mother is awasherwoman . My father earns about 25 dollars a day and my mother is getting about fiftydollars a month . Though poor , ours is a happy family . My parents seldom quarrel and they arethrifty .
All my brothers and sisters are studying in English schools . My eldest brother Ronnie isstudying in secondary four in a government school . He says that he will pass this year , with four good credits at least .
On school days my brother goes to school by bus and we children are in a nearby primary schoolnot very far from our home .
During the week-end my eldest brother helps us with our studies .

minh ơi, mày còn nhanh hơn tao >o<

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