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Choose the letter A, B, C or D to answer these following questions

Robots through the Middle Ages were used primarily for entertainment. However, the 20th century featured a boom in the development of industrial robots. Industry has benefited drastically from the expanse of a robotic work force. Automated machines have taken over dangerous and boring jobs from humans. Because robots never get tired, extra shifts have been added to factories. Farmers have taken advantage of new technology with automated harvesters. The medical industry benefits from advancements in assisted surgical robotics. The military has launched various programs in robotic technology.

Question: What have automated machines done for human?

A. They do household chores.

B. They build houses and buildings.

C. They do dangerous and boring jobs.

D. They make food and drink.

Biến đổi vế A ta có

\(A=\)\(1+3+3^2+3^3+3^4+3^5+3^6\)

\(3\)\(A=3.\left(1+3+3^2+3^3+3^{\text{4}}+3^{\text{5}}+3^6\right)\)

\(3\)\(A=3+3^2+3^3+3^4+3^5+3^6+3^7\)

\(3A-A=\left(3+3^2+3^3+...+3^7\right)-\left(1+3+3^2+3^3+...+3^6\right)\)\(2A=3^7-1\)

\(A=\dfrac{3^7-1}{2}\)

bạn tick cho mik nhé !!! mà cậu sai đề bài hay sao ý phải là B=\(\dfrac{3^7-1}{2}\) thui cậu tự so sánh nhé