Hello, everybody! Allow me to introduce myself. My name is Hai, I am 13 years old and a student at Gia Thụy secondary school . My favorite subject is math. I was born and grew up in Ha Noi. At the moment, I am living with my parents and a younger brother.I am a quiet, a little bit childish but also factual, dexterous and roman lady. In the education views, I am diligent, clever and patient with my study or even work and I never give up even though I know a lot of hardships are waiting for me in the future. My hobbies are jewellery collections, taking a walk in the afternoon, listening to music and watching movies. Parularly, I really love to watch how to make a sweet cake videos from the internet. I also enjoy playing badminton and riding a bicycle.My dream is to be a successful business woman so that now I am trying to study as hard as I can to get into the right subject that I love. And I also hope that my dream will come true and surely I will do everything to make it come true.

ngày hôm qua làm việc của mình chi chi đó nà

\(D=\frac{5}{1+2+3}+\frac{5}{1+2+3+4}+...+\frac{5}{1+2+...+100}\)

\(\Rightarrow D=5\left(\frac{1}{1+2+3}+\frac{1}{1+2+3+4}+...+\frac{1}{1+2+...+100}\right)\)

\(\Rightarrow D=5\left(\frac{1}{\frac{4.3}{2}}+\frac{1}{\frac{5.4}{2}}+...+\frac{1}{\frac{101.100}{2}}\right)\)

\(\Rightarrow D=5\left(\frac{2}{3.4}+\frac{2}{4.5}+...+\frac{2}{100.101}\right)\)

\(\Rightarrow D=10\left(\frac{1}{3}-\frac{1}{4}+\frac{1}{4}-\frac{1}{5}+...+\frac{1}{100}-\frac{1}{101}\right)\)

\(\Rightarrow D=10\left(\frac{1}{3}-\frac{1}{101}\right)\)

\(\Rightarrow D=\frac{10}{3}-\frac{10}{101}=\frac{980}{303}\)

I don't now

or no I don't

..................

sorry

a: Xét tứ giác AEHF có 

\(\widehat{AEH}=\widehat{AFH}=\widehat{FAE}=90^0\)

Do đó: AEHF là hình chữ nhật

Mình đang cần gấp. Các bạn giúp mình nha. Mình cảm ơn các bạn rất nhiều ạ!

đáp án "E" nha,k cho mik nha