Đáp án:
$\begin{array}{l}
a)\left( {246 - 567} \right) - \left( {245 + 123} \right) + \left( {567 - 123} \right)\\
= 246 - 567 - 245 - 123 + 567 - 123\\
= \left( {246 - 245} \right) - \left( {123 + 123} \right) + \left( {567 - 567} \right)\\
= 1 - 246\\
= - 245\\
b){135.35.35^2}\\
= 5788125\\
c)1234.\left( { - 123} \right) - 123.34 + 123.\left( { - 268} \right)\\
= 123.\left( {1234 - 34 - 268} \right)\\
= 123.\left( {1200 - 268} \right)\\
= 123.932\\
= 114636\\
d)S = \left( { - 2} \right) - {\left( { - 2} \right)^2} + {\left( { - 2} \right)^3} - {\left( { - 2} \right)^4} + {\left( { - 2} \right)^5}\\
- ... + {\left( { - 2} \right)^{2019}} - {\left( { - 2} \right)^{2020}}\\
\Rightarrow \left( { - 2} \right).S = {\left( { - 2} \right)^2} - {\left( { - 2} \right)^3} + {\left( { - 2} \right)^4} - ... + {\left( { - 2} \right)^{2020}} - {\left( { - 2} \right)^{2021}}\\
\Rightarrow S + \left( { - 2} \right)S = - 2 - {\left( { - 2} \right)^{2021}} = - 2 + {2^{2021}}\\
\Rightarrow - S = {2^{2021}} - 2\\
\Rightarrow S = 2 - {2^{2021}}
\end{array}$
