[Amankris]

ลอง Telescope ตัวนี้ดู

4). Simplify $\dfrac{3^3}{2}-\dfrac{5^3}{6}+\dfrac{7^3}{12}-\dfrac{9^3}{20}+\dfrac{11^3}{30}-\dfrac{13^3}{42}+\dfrac{15^3}{56}-\dfrac{17^3}{72}+\ldots+\dfrac{199^3}{9900}$