Ta có : \(12^{100}+19^{21}=12^{4.25}+19^{20+1}\)

\(=\left(12^4\right)^{25}+19^{20}.19\)

\(=\left(...6\right)^{25}+19^{4.5}.19\)

\(=\left(...6\right)+\left(19^4\right)^5.19\)

\(=\left(...6\right)+\left(...1\right)^5.19\\\)

\(=\left(...6\right)+\left(...1\right).19\)

\(=\left(...6\right)+\left(...9\right)\)

\(=\left(...5\right)chiahếtcho5\)

=> 12^100 + 19^21 chia hết cho 5 ( điều phải chứng minh )

Chúc bạn học tốt!

Đề bài : Talk about your friend.

Hi everyone! My name is Annie. I'm eleven years old. I live in Vinh Thanh commune. Now I'm telling about my friend.

My friend is very nice. And she is my best friend. Her name is Andrena. She is eleven years old and she is my classmate. You can call her "Bunny". She lives in Vinh Thanh commune, too. She is shorter than me. She has long black hair. Andrena's eyes are sparkling. She has a round face and chubby cheeks. She always has a friendly smile when she meets friends.I usually make mistakes in mathematics, she sometimes helps me with my homework. So Andrena is very clever and kind. And she is also a creative girl, because she can writes poems very well. At break time, we regularly play together.

Andrena is a good friend. I love my friend so much! How about you? What does your friend look like?

90,9% muốn bt cách giải tick cái

Ta có: a/5 = b/4 = c/3

           =>a³/125 = b³/64 = c³/27= a.b.c/5.4.3 = -480/60 = -8

           =>a³=-8.125= -1000 = -10³ =>a= -10

               b³=-8.64= -512 = -8³   =>b= -8

               c³= -8.27= -216 = -6³ =>c=-6