SEAMO 2027 - Paper C - SET 10 - Self-study Question 15

Evaluate $\displaystyle\left(1+\frac12+\frac13+\cdots+\frac1{2025}\right)\left(\frac12+\frac13+\cdots+\frac1{2026}\right)-\left(1+\frac12+\frac13+\cdots+\frac1{2026}\right)\left(\frac12+\frac13+\cdots+\frac1{2025}\right)$.