Explicație pas cu pas:
[tex]9 \cdot (5 + 10 + 15 + ... + 200) \div 41 = \\ 9 \cdot5 \cdot(1 + 2 + 3 + ... + 40) \div 41 = \\ 9 \cdot5 \cdot \frac{40 \cdot41 }{2} \div 41 = \\ 9 \cdot5 \cdot20 \cdot41 \div 41 = \\ 9 \cdot5 \cdot20 = {3}^{2} \cdot5 \cdot5 \cdot4 = \\ {3}^{2} \cdot {5}^{2} \cdot {2}^{2} = {(3 \cdot5 \cdot2)}^{2} = {30}^{2} [/tex]
