\frac 1 9 %2B \frac 1 6 %2B \frac 1 12 %2B \fr

1.	\frac 1 9 %2B \frac 1 6 %2B \frac 1 12 %2B \frac 1 20 %2B \frac 1 30 %2B \frac 1 42 %2B \frac 1 56 %2B \frac 1 72
Answer» 1/9 + 1/6 + 1/12 + 1/30 + 1/42+ 1/56 + 1/72 = 1/9 + 1/2 - 1/3 + 1/3 - 1/4 + 1/4 - 1/5 + 1/5 - 1/6 + 1/6 - 1/7 + 1/7 - 1/8 + 1/8 - 1/9 = 1/2 + (1/9-1/9) + (1/3 - 1/3) + (1/4 - 1/4) + (1/5 - 1/5) + (1/6 - 1/6) + (1/7 - 1/7) + (1/8 - 1/8) = 1/2 + 0 = 1/2

\frac 1 9 %2B \frac 1 6 %2B \frac 1 12 %2B \frac 1 20 %2B \frac 1 30 %2B \frac 1 42 %2B \frac 1 56 %2B \frac 1 72

Answer»

1/9 + 1/6 + 1/12 + 1/30 + 1/42+ 1/56 + 1/72

= 1/9 + 1/2 - 1/3 + 1/3 - 1/4 + 1/4 - 1/5 + 1/5 - 1/6 + 1/6 - 1/7 + 1/7 - 1/8 + 1/8 - 1/9

= 1/2 + (1/9-1/9) + (1/3 - 1/3) + (1/4 - 1/4) + (1/5 - 1/5) + (1/6 - 1/6) + (1/7 - 1/7) + (1/8 - 1/8)

= 1/2 + 0

= 1/2