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D= 1/1 - 1 /2 + 1/2 - 1/4 + 1/4 - 1/7 +...+ 1/46 - 1/56

D= 1/1 - 1/56

D=  55/56

vậy D= 55/56

\(P=1-\frac{1}{2}+\frac{1}{2}-\frac{1}{4}+\frac{1}{4}-\frac{1}{7}+...+\frac{1}{46}-\frac{1}{56}\)

\(P=1-\frac{1}{56}\)

\(P=\frac{55}{56}\)

P=\(1-\frac{1}{2}+\frac{1}{2}-\frac{1}{4}+\frac{1}{4}-\frac{1}{7}+...+\frac{1}{46}-\frac{1}{56}\)

P=\(1-\frac{1}{56}\)

P=\(\frac{55}{56}\)

P = 1 - 1/2 + 1/2 - 1/4 +.......+1/46 - 1/56

P = 1 - 1/56

P = 55/56 nha!

dễ thôi 

P= 1/1.2 + 2/2.4 + 3/4.7 + ... + 10/46.56 

P= 1- 1/2 + 1/2 - 1/4 + 1/4 -1/7 +... + 1/46 - 1/56

P=1 - 1/56

P=55/56

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-\(\frac{1}{56}\)=\(\frac{55}{56}\)

Pò Sữa,  3/4.7  tách ra sao ?

P=1-\(\frac{1}{2}\)+\(\frac{1}{2}\)-\(\frac{1}{4}\)+...........+\(\frac{1}{46}\)-\(\frac{1}{56}\)

P=1-\(\frac{1}{56}\)

P=\(\frac{55}{56}\)

p=55/56

=1/1-1/2+1/2-1/4+...+1/46-1/56

=1-1/56

55/56

\(P=\frac{1}{1\cdot2}+\frac{2}{2\cdot4}+\frac{3}{4\cdot7}+...+\frac{10}{46\cdot56}\)

\(\Rightarrow P=1-\frac{1}{2}+\frac{1}{2}-\frac{1}{4}+\frac{1}{4}-\frac{1}{7}+...+\frac{1}{46}-\frac{1}{56}\)

\(\Rightarrow P=1-\frac{1}{56}\)

\(\Rightarrow P=\frac{55}{56}\)

1/1.2+2/2.4+3/4.7+...+10/46/56

=1-1/2+1/2-1/4+1/4-1/7+...+1/46-1/56

=1-1/56

=55/56

1/1.2+2/2.4+3/4.7+...+10/46.56

=1-1/2+1/2-1/4+1/4-1/7+...+1/46-1/56 

=1-1/56

=55/56