C

D

Câu 49:C

Câu 50:D

C

D

( 4,5 - \(\dfrac{4}{7}\) \(x\)): \(\dfrac{5}{6}\) = 0,6

(4,5 - \(\dfrac{4}{7}\)\(x\)) = 0,6 \(\times\) \(\dfrac{5}{6}\)

4,5 - \(\dfrac{4}{7}\) \(x\) = 0,5

          \(\dfrac{4}{7}x\) = 4,5 - 0,5

            \(\dfrac{4}{7}x\) = 4

               \(x\) = 4 : \(\dfrac{4}{7}\)

               \(x\) = 7

Cảm ơn ạ

A

A

A nha 

\(21_{10}=10101_2\)

a) \(A=12\left(83+17\right)=12.100=1200\)

b) \(B=-11\)

c) \(C=14+50=64\)

d) \(D=35-35+45=45\)

\(\Rightarrow A=\dfrac{1}{\left(2\cdot2\right)^2}+\dfrac{1}{\left(2\cdot3\right)^2}+\dfrac{1}{\left(2\cdot4\right)^2}+...+\dfrac{1}{\left(2n\right)^2}\\ A=\dfrac{1}{4}\left(\dfrac{1}{2^2}+\dfrac{1}{3^2}+\dfrac{1}{4^2}+...+\dfrac{1}{n^2}\right)< \dfrac{1}{4}\left(\dfrac{1}{1\cdot2}+\dfrac{1}{2\cdot3}+\dfrac{1}{3\cdot4}+...+\dfrac{1}{\left(n-1\right)n}\right)\\ A< \dfrac{1}{4}\left(1-\dfrac{1}{2}+\dfrac{1}{2}-\dfrac{1}{3}+\dfrac{1}{3}-\dfrac{1}{4}+...+\dfrac{1}{\left(n-1\right)}-\dfrac{1}{n}\right)\\ A< \dfrac{1}{4}\left(1-\dfrac{1}{n}\right)< \dfrac{1}{4}\left(\text{đ}pcm\right)\)

bài hình mà không gửi hình, làm bài = niềm tin hả bạn