Bài toán: Chứng minh rằng: $\text{S =}$ $\frac{1}{2^{2}}$ $\text{-}$ $\frac{1}{2^{4}}$ $\text{+}$ $\frac{1}{2^{6}}$ $\text{-}$ $\text{...}$ $\text{+}$ $\frac{1}{2^{4n - 2}}$ $\text{-}$ $\frac{1}{2^{4n}}$ $\text{+}$ $\text{...}$ $\text{+}$ $\frac{1}{2^{2002}}$ $\text{-}$ $\frac{1}{2^{2004}}$ $\text{<}$ $\text{0,2}$

What does the doctor recommend to eat?

What do happy people do? 

What kind of food will help people to keep fit and stay healthy?