a) 17+25+13+45=100

=(17+13)+(25+45)=30+70=100

a) 17+ 25 + 13 + 45

= ( 17+ 13)+(25+ 45)

=  30 + 70

= 100

đăng câu linh tinh nhiều thế bạn ,nhưng kb thì kb thôi -_-"

mk nè k mình nha

mk nha

cố lên 

VN vô địch

đương nhiên rồi,chắc chắn VIỆT NAM sẽ thắng mà bn Buồn của em

 As you know, there are many festivals around the world now and I think each festival has their own special things. But the festival I love best is Japan Summer Festival. I enjoyed this festival with my family in Japan last week. It was very wonderful. This festival had a lot of activities for people to attend. The outdoor activities and the interesting atmosphere are the most exciting in the festival. Everybody wore kimono or yukata to join the Summer Festival. It's a traditional clothes of Japanese. Anh of course I wore a kimono to take part in the festival. There, everyone can play and enjoy the festival together. I think it made people closer. What a wonderful memory! I love Japane so much.

ở MB nước ta thôi

 As you know, Viet Nam has many traditional festivals and each festival is very special. But among these festivals, I love Tet best because of many reasons. And Tet was the latest festival I have joined recently. For me, Tet is the wonderful time for family because they can be closer. Befor Tet, I and my family cleaned and decorated our house with peach blossoms, colourful lights. On the first days of Tet, I wore many beautiful new clothes to visit my grandparents and my relatives. I got lucky money from them, too. Tet is so great, isn't it?

Bạn vào link này nhé:https://h.vn/hoi-dap/question/39236.html

~Study well~

#Bạch_Dương_Chi#

\(B=\frac{1+2+2^2+2^3+...+2^{2008}}{1-2^{2009}}\)

Đặt: \(A=1+2+2^2+2^3+....+2^{2008}\)

\(\Rightarrow2A=2+2^2+2^3+2^4+...+2^{2009}\)

\(\Rightarrow2A-A=\left(2+2^2+2^3+2^4+...+2^{2009}\right)-\left(1+2+2^2+2^3+....+2^{2008}\right)\)

\(\Rightarrow2^{2009}-1\)

\(\Rightarrow B=\frac{2^{2009}-1}{1-2^{2009}}\)

Đặt \(A=1+2+2^2+2^3+...+2^{2008}\)

\(\Rightarrow2A=2+2^2+2^3+2^4...+2^{2009}\)

\(\Rightarrow2A-A=2+2^2+2^3+2^4...+2^{2009}-1-2-2^2-2^3-...-2^{2008}\)

\(\Rightarrow A=2^{2009}-1\)

\(\Rightarrow B=\frac{2^{2009}-1}{1-2^{2009}}=\frac{-1\left(1-2^{2009}\right)}{1-2^{2009}}=-1\)

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