[Puriwatt]

จงหาค่าผลบวกของอนุกรมต่อไปนี้
ข้อ 1. $$51+53+55+57++59+...+199$$
ข้อ 2. $$\frac {3}{1\times2^2} +\frac{5}{2^2\times3^2}+\frac{7}{3^2\times4^2}+\frac{9}{4^2\times5^2}+...+\frac{199}{99^2\times100^2}$$
ข้อ 3. $$\frac {1}{1+\sqrt{2}} + \frac{1}{\sqrt{2}+\sqrt{3}} + \frac{1}{\sqrt{3}+\sqrt{4}}+\frac{1}{\sqrt{4}+\sqrt{5}}+...+\frac{1}{\sqrt{9999}+\sqrt{10000}}$$
ข้อ 4. $$\frac {1}{2+\sqrt{2}} + \frac{1}{3\sqrt{2}+2\sqrt{3}} + \frac{1}{4\sqrt{3}+3\sqrt{4}}+\frac{1}{5\sqrt{4}+4\sqrt{5}}+...+\frac{1}{10000\sqrt{9999}+9999\sqrt{10000}}$$