Question

Đã trả lời bởi chuyên gia

Answer 1

\[\begin{array}{*{20}{l}}
\begin{array}{l}
a.{\rm{ }}1 - 2 + 3 - {\rm{ }}4 + {\rm{ }}5 - 6 + ... + 2019{\rm{ }} - {\rm{ }}2020\\
= {\rm{ }}\left( {1 - 2} \right) + \left( {3 - {\rm{ }}4} \right) + {\rm{ }}\left( {5 - 6} \right) + ... + \left( {2019{\rm{ }} - {\rm{ }}2020} \right)\\
= \left( { - 1} \right) + \left( { - 1} \right) + \left( { - 1} \right) + ... + \left( { - 1} \right)\\
= \left( { - 1} \right).1010\\
= - 1010
\end{array}\\
\begin{array}{l}
b.{\rm{ }}1 + \left( { - 3} \right) + 2 + \left( { - 4} \right) + 3 + \left( { - 5} \right) + ... + 18 + \left( { - 20} \right)\\
= \left( {1 - 3} \right) + \left( {2 - 4} \right) + .... + \left( {18 - 20} \right)\\
= \left( { - 2} \right) + \left( { - 2} \right) + ... + \left( { - 2} \right)\\
= \left( { - 2} \right).18\\
= - 36
\end{array}\\
\begin{array}{l}
c.{\rm{ }} - 1 + 2{\rm{ }} - 3 + {\rm{ }}4{\rm{ }} - {\rm{ }}5 + 6{\rm{ }} - ... - {\rm{ }}2019{\rm{ }} + {\rm{ }}2020{\rm{ }} - {\rm{ }}2021\\
= \left( { - 1 + 2} \right) + \left( { - 3 + 4} \right) + \left( { - 5 + 6} \right) + ... + \left( { - 2019 + 2020} \right) - 2021\\
= 1 + 1 + 1 + ... + 1 - 2021\\
= 1.2019 - 2021\\
= 2019 - 2021\\
= - 2\;
\end{array}\\
\begin{array}{l}
d.{\rm{ }}1 + 2 - 3 - {\rm{ }}4{\rm{ }} + 5 + 6 - 7 - 8 + ... + {\rm{ }}2018{\rm{ }}--{\rm{ }}2019{\rm{ - }}2020 + 2021\\
= {\rm{ }}\left( {1 + 2 - 3 - {\rm{ }}4{\rm{ }}} \right) + \left( {5 + 6 - 7 - 8} \right) + ... + \left( {2017 + 2018 - 2019 - 2020} \right) + 2021\\
= \left( { - 4} \right) + \left( { - 4} \right) + ... + \left( { - 4} \right) + 2021\\
= \left( { - 4} \right).505 + 2021\\
= - 2020 + 2021\\
= 1
\end{array}
\end{array}\]

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Answer 2

\[\begin{array}{*{20}{l}}
\begin{array}{l}
a.{\rm{ }}1 - 2 + 3 - {\rm{ }}4 + {\rm{ }}5 - 6 + ... + 2019{\rm{ }} - {\rm{ }}2020\\
= {\rm{ }}\left( {1 - 2} \right) + \left( {3 - {\rm{ }}4} \right) + {\rm{ }}\left( {5 - 6} \right) + ... + \left( {2019{\rm{ }} - {\rm{ }}2020} \right)\\
= \left( { - 1} \right) + \left( { - 1} \right) + \left( { - 1} \right) + ... + \left( { - 1} \right)\\
= \left( { - 1} \right).1010\\
= - 1010
\end{array}\\
\begin{array}{l}
b.{\rm{ }}1 + \left( { - 3} \right) + 2 + \left( { - 4} \right) + 3 + \left( { - 5} \right) + ... + 18 + \left( { - 20} \right)\\
= \left( {1 - 3} \right) + \left( {2 - 4} \right) + .... + \left( {18 - 20} \right)\\
= \left( { - 2} \right) + \left( { - 2} \right) + ... + \left( { - 2} \right)\\
= \left( { - 2} \right).18\\
= - 36
\end{array}\\
\begin{array}{l}
c.{\rm{ }} - 1 + 2{\rm{ }} - 3 + {\rm{ }}4{\rm{ }} - {\rm{ }}5 + 6{\rm{ }} - ... - {\rm{ }}2019{\rm{ }} + {\rm{ }}2020{\rm{ }} - {\rm{ }}2021\\
= \left( { - 1 + 2} \right) + \left( { - 3 + 4} \right) + \left( { - 5 + 6} \right) + ... + \left( { - 2019 + 2020} \right) - 2021\\
= 1 + 1 + 1 + ... + 1 - 2021\\
= 1.2019 - 2021\\
= 2019 - 2021\\
= - 2\;
\end{array}\\
\begin{array}{l}
d.{\rm{ }}1 + 2 - 3 - {\rm{ }}4{\rm{ }} + 5 + 6 - 7 - 8 + ... + {\rm{ }}2018{\rm{ }}--{\rm{ }}2019{\rm{ - }}2020 + 2021\\
= {\rm{ }}\left( {1 + 2 - 3 - {\rm{ }}4{\rm{ }}} \right) + \left( {5 + 6 - 7 - 8} \right) + ... + \left( {2017 + 2018 - 2019 - 2020} \right) + 2021\\
= \left( { - 4} \right) + \left( { - 4} \right) + ... + \left( { - 4} \right) + 2021\\
= \left( { - 4} \right).505 + 2021\\
= - 2020 + 2021\\
= 1
\end{array}
\end{array}\]

Answer 3

a.1−2+3−4+5−6+...+2019−2020=(1−2)+(3−4)+(5−6)+...+(2019−2020)=(−1)+(−1)+(−1)+...+(−1)=(−1).1010=−1010b.1+(−3)+2+(−4)+3+(−5)+...+18+(−20)=(1−3)+(2−4)+....+(18−20)=(−2)+(−2)+...+(−2)=(−2).18=−36c.−1+2−3+4−5+6−...−2019+2020−2021=(−1+2)+(−3+4)+(−5+6)+...+(−2019+2020)−2021=1+1+1+...+1−2021=1.2019−2021=2019−2021=−2d.1+2−3−4+5+6−7−8+...+2018−−2019−2020+2021=(1+2−3−4)+(5+6−7−8)+...+(2017+2018−2019−2020)+2021=(−4)+(−4)+...+(−4)+2021=(−4).505+2021=−2020+2021=1

Số thứ tự	Loại hàng	Số lượng (quyển)	Giá đơn vị (đồng)	Tổng số tiền (đồng)
1	Vở loại 1	35	2000	...
2	Vở loại 2	42	1500	...
3	Vở loại 3	38	1200	...
Cộng:				...

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