Không quy đồng hãy tính hợp lý các tổng sau :

a) \(A=\dfrac{-1}{20}+\dfrac{-1}{30}+\dfrac{-1}{42}+\dfrac{-1}{56}+\dfrac{-1}{72}+\dfrac{-1}{90}\)

b) \(B=\dfrac{5}{2.1}+\dfrac{4}{1.11}+\dfrac{3}{11.2}+\dfrac{1}{2.15}+\dfrac{13}{15.4}\)

rút gọn phân số sau : \(\dfrac{\left(-2\right)^3.3^3.5^3.7.8}{3.5^3.2^4.42}\)

viết câu nghĩa ko đổi :

1.Nam is interested in watching television .

-> Nam likes .............................

2.The children want to watch cartoon on television .

-> The children would ...................

3.There isn't any sugar in the coffee .

-> The coffee ...........................