Đáp án:
P = 16872
Giải thích các bước giải:
\[\begin{array}{l}P = {\rm{ }}1.2 + 2.3 + 3.4 + ... + 36.37{\rm{ }}\\3P = {\rm{ }}1.2.3{\rm{ }} + 2.3.3 + 3.4.3 + ... + 36.37.3{\rm{ }}\\\,\,\,\,\,\,\, = 1.2.\left( {3 - 0} \right) + 2.3.\left( {4 - 1} \right) + 3.4.\left( {5 - 2} \right) + ... + 36.37.\left( {38 - 35} \right){\rm{ }}\\\,\,\,\,\,\,\, = {\rm{ }}\left( {1.2.3 + 2.3.4 + 3.4.5 + ... + 36.37.38} \right) - \left( {0.1.2 + 1.2.3 + 2.3.4 + ... + 35.36.37} \right){\rm{ }}\\\,\,\,\,\,\,\, = {\rm{ }}36.37.38 - 0.1.2\\\,\,\,\,\,\,\, = 36.37.38{\rm{ }}\\ \Rightarrow P = \frac{{36.37.38}}{3}\\ \Rightarrow P = 16872\end{array}\]
