\(\left(-2021\right).\left(23+76\right)-2021=\left(-2021\right).99-2021=-202100\)

=-2021x100=-202100

\(5,-\dfrac{2}{7}-\left(\dfrac{5}{11}-\dfrac{9}{7}\right)+\dfrac{5}{11}=-\dfrac{2}{7}-\dfrac{5}{11}+\dfrac{9}{7}+\dfrac{5}{11}=\left(-\dfrac{2}{7}+\dfrac{9}{7}\right)-\left(\dfrac{5}{11}-\dfrac{5}{11}\right)=1-0=1\\ 6,\dfrac{2}{3}+\dfrac{-2}{5}+\dfrac{-5}{6}-\dfrac{13}{10}=\left(\dfrac{4}{6}+\dfrac{-5}{6}\right)+\left(\dfrac{-4}{10}-\dfrac{13}{10}\right)=\dfrac{-1}{6}+\dfrac{-17}{10}=\dfrac{-5}{30}+\dfrac{-51}{30}=\dfrac{-56}{30}=\dfrac{-28}{15}\)

\(7,\dfrac{-5}{9}+\dfrac{8}{15}+\dfrac{4}{-9}+\dfrac{7}{15}=\left(\dfrac{-5}{9}+\dfrac{-4}{9}\right)+\left(\dfrac{8}{15}+\dfrac{7}{15}\right)=\left(-1\right)+1=0\\ 8,\left(\dfrac{12}{13}+7\right)-\left(-\dfrac{1}{13}+8\right)=\dfrac{12}{13}+7+\dfrac{1}{13}-8=\left(\dfrac{12}{13}+\dfrac{1}{13}\right)+\left(7-8\right)=1+\left(-1\right)=0\)

122/456

Hịb

25.8.4.28.125

= 28.(25.4).(8.125)

= 28.100.1000

= 2800.1000

= 2800000

Tham khảo: https://hoc247.net/hoi-dap/toan-6/tinh-a-b-voi-a-34-7-13-51-13-22-85-22-37-68-37-49-faq162600.html

\(C=\left(\dfrac{12}{199}+\dfrac{23}{200}-\dfrac{34}{201}\right).\left(\dfrac{1}{2}-\dfrac{1}{3}-\dfrac{1}{6}\right)\)

\(C=\left(\dfrac{12}{199}+\dfrac{23}{200}-\dfrac{34}{201}\right).0\)

\(C=0\)

Bn ơi, bị lỗi ảnh rồi.

lỗi rồi bạn 

\(12,25+\left(-21,37\right)-\left(14,67-21,75\right)\)

\(=12,25-21,37-14,67+21,75\)

\(=12,25+21,75-21,37-14,63-0,04\)

\(=34-36-0,04\)

= -2-0,04=-2,04

120:{54-[50:2.(3^2-2.4)]}

= 120:{ 54-[25.(9-8)]}

= 120:{54-[25.1]}

= 120:{54-25}

= 120:29

=\(\dfrac{120}{29}\)