Bài 1: Thực hiện phép tính
\(\begin{array}{l}a)\,13 + \left| { - 17} \right| - 12\\ = 13 - 12 + 17\\ = \,\,\,1 + 17\\ = 18\end{array}\)
\(\begin{array}{l}b)\,\left( {90:3 - 11} \right) + 15.3 + 15.7\\ = \left( {30 - 11} \right) + 15.\left( {3 + 7} \right)\\ = 19 + 150\\ = 169\end{array}\)
\(\begin{array}{l}c)\,{3^2}.4 - 128:{2^3}\\ = 9.4 - 128:8\\ = \,\,36 - 16\\ = - 20\end{array}\)
\(\begin{array}{l}d)\,12.49 + 154 + \left( { - 249} \right) + \left( { - 56} \right)\\ = 588 + 154 - 249 - 56\\ = 437\end{array}\)
Bài 3:
\(\begin{array}{l}M = 9 + {3^2} + {3^3} + {3^4} + ... + {3^{30}}\\3.M = 3.9 + {3^3} + {3^4} + {3^5} + ... + {3^{31}}\\2M = 3M - M = {3^{31}} + 3.9 - {3^2} - 9\\2M = {3^{31}} - 9\\ \Rightarrow M = \frac{{{3^{31}} - 9}}{2}\end{array}\)