a: Xét ΔBHD vuông tại H và ΔENC vuông tại N có

BD=EC

\(\widehat{BDH}=\widehat{ECN}\)

Do đó: ΔBHD=ΔENC

\(=\dfrac{\left[\dfrac{2}{3}\cdot\left(-\dfrac{3}{4}\right)\right]^2\cdot\dfrac{2}{3}\cdot\left(-1\right)}{\left[\dfrac{2}{5}\cdot\left(\dfrac{-5}{12}\right)\right]^2\left(-\dfrac{5}{12}\right)}=\dfrac{\left(-\dfrac{1}{2}\right)^2\left(-\dfrac{2}{3}\right)}{\left(-\dfrac{1}{6}\right)^2\left(-\dfrac{5}{12}\right)}\\ =\dfrac{\dfrac{1}{4}\left(-\dfrac{2}{3}\right)}{\dfrac{1}{36}\left(-\dfrac{5}{12}\right)}=\left(-\dfrac{1}{6}\right):\left(-\dfrac{5}{432}\right)=\dfrac{72}{5}\)

​3^42 : 2^81 = 3^:(2^2)

suy ra 3^42 < 2^81

mình đúng nhớ cho điểm đó

MIK KO HIỂU BẠN CÓ THỂ GIẢI CỤ THỂ HƠN KO

QUA DE 3^42 > 2^81 CHAC CHAN DO

ta thấy 1978 ko chia hết cho 11 

78 ko chia hết cho 11 suy ra a chia hết cho 11

2012 ko chia het cho 11

10 ko chia het cho 11

suy ra chắc chắn b chia hết cho 11 ( ĐPCM)

k nha

\(1978a+2012b-78a-10b=1900a+2002\)

ma 2002b chia het cho 11

=>1900a chia het cho 11 nhung 1900 khong chia het cho 11

=>a chia het cho 11 (1)

ta co 78a+10b chia het cho 11 ma 78a chia het cho 11

=>10b chia het cho 11 ma 10 khong chia het cho 11

=>b chia het cho 11 (2)

tu (1) va (2) =>a+b chia het cho 11

cho xin loi 2002 thanh 2002b

Số cần tìm bớt đi 1 đơn vị được số mới chia hết cho 2; 3; 5; 7

Số mới là

2x3x5x7=210

Số cần tìm là

210+1=211

\(\frac{\left(25-15\right)^2-\left(-35\right)}{15-\left(2^0+2^3\right)}=\frac{135}{6}=\frac{45}{2}\)

đáp án của mình là 82,62+11,49=94,11

đúng thì k cho mình nha

82,72 + 11,43 = 94,15

ai làm ra cách làm thì mình mới k

My best friend is my classmate at school. She and I have been studying together since we entered school in kindergarten. We have studied together all these years. We also travel by the school bus together because we stay close to each other. Her home is only a ten minute walk from my place.My friend is kindly and sweet-natured. We are always happy to ewith each other. We enjoy studying, playing and eating together. If I am sad she will do all she can to make me smile and feel happy.She has always been kind and helpful to me. When I miss school because I am unwell she comes to my place to share with me all that has been done at school. When she misses school I too help her with all that has been covered at school. We also play badminton together in the evenings.

I have a best friend named Linh, we have been together since we were just little kids. She has beautiful bright skin and brown eyes. We have a lot of things in common, such as we love the same band, food and books. She and I even share the same name, and it is a small surprise for anyone who has talked to us. Linh is not my classmate, but we always help each other with the homework and school projects. We spend every minute in our break time to talk about all the things that happen in class, and people usually ask what can even makes us laugh that hard. Sometimes I think it is we have been best mates since forever, and I hope that we will be happy this for a very long time.

I and Khai are team mates in our school’s soccer team, and that is the reason we became best friends. At first we did not know each other, but we quickly became close after just a few weeks. Khai is a good player, so he always helps me prace to improve my skills. In order to thank him, I become his instructor in some of the subjects in class. I am as tall and slim as Khai, and many people say that we look brothers. In fact, we are even closer than brothers. We can share almost everything, from feelings to clothes and hobbies. I always proud of our friend ship, and we will keep it this as long as we can.