\(D=2.4+4.6+...+98.100\)
\(\Rightarrow6D=2.4.6+4.6.6+...+98.100.6\)
\(=2.4.6+4.6.\left(8-2\right)+...+98.100.\left(102-96\right)\)
\(=2.4.6-2.4.6+4.6.8+...+98.100.102-96.98.100\)
\(=98.100.102\)
\(=999600\)
\(\Rightarrow D=\frac{999600}{6}=166600\)
\(D=2.4+4.6+...+98.100\)
\(6D=2.4.6+4.6.6+...+98.100.6\)
\(=2.4.6+4.6.\left(8-2\right)+...+98.100.\left(102-96\right)\)
\(=2.4.6-2.4.6+4.6.8+...+98.100.102\)
\(=98.100.102\)
\(6D=999600\)
\(D=999600:6\)
\(D=166600\)
\(D=2\left(1.2+2.3+49.50\right)\)
\(\Leftrightarrow3D=1.2.3+2.3.3+...+49.50.3\)
\(=1.2.3+2.3.\left(4-1\right)+3.4.\left(5-2\right)+...+49.50.\left(51-48\right)\)
\(=1.2.3+2.3.4-1.2.3+...+49.50.51-48.49.50\)
\(3D=49.50.51\Rightarrow D=\frac{49.50.51}{3}=41650\)
Vậy\(D=41650\)
Các bạn đổi 3D thành 1,5D hộ mình nhé!
