mk đang cần gấp
\(D=1-\frac{1}{4}+\frac{1}{4}-\frac{1}{7}+\frac{1}{7}-\frac{1}{10}+...+\frac{1}{97}-\frac{1}{100}\)
\(D=1-\frac{1}{100}\)
\(D=\frac{99}{100}\)
tại sao lại như thế?
D = 3/1x4 + 3/4x7 + 3/7x10 + ......+ 3/97x100
= 4-1/1x4 + 7-4/4x7 + 10-7/7x10 + ...... + 100-97/97x100
= 4/1x4 - 1/1x4 + 7/4x7 - 4/4x7 + 10/7x10 - 7/7x10 + ........+ 100/97x100 - 97/97 x 100
= 1 - 1/4 + 1/4 - 1/7 + 1/7 -1/10 + ........+ 1/97 - 1/100
= 1 - 1/100
= 99/100
