P= 1/1 -1/2 + 1/2 -1/4 + 1/4 - 1/7 +....+ 1/46 -1/56
P= 1/1 - 1/56
=> P= 55/ 56
Có \(\frac{1}{1.2}=\frac{1}{1}-\frac{1}{2}\)
\(\frac{2}{2.4}=\frac{1}{2}-\frac{1}{4}\)......................... tương tự đến \(\frac{10}{46.56}=\frac{1}{46}-\frac{1}{56}\)
suy ra P= 1-\(\frac{1}{56}\)=\(\frac{55}{56}\)