A hint for "A Neat Trick" 

\( 1+2+3= \frac{3 \times 4}{2}\)

\( 1+2+3+4= \frac{4 \times 5}{2}\)

\(1+2+3+4+5= \frac{5 \times 6}{2}  \)

Do you see the pattern?  Does it always work?  Why?

---

---