Question

[Đàm Mai Hoa]

tính nhanh: 1-5/6+7/12-9/20+11/30-13/42+15/56-17/72+19/90

Answer 1

[subjects]

\(1-\dfrac{5}{6}+\dfrac{7}{12}-\dfrac{9}{20}+\dfrac{11}{30}-\dfrac{13}{42}+\dfrac{15}{56}-\dfrac{17}{72}+\dfrac{19}{90}\\ =1-\dfrac{5}{2\cdot3}+\dfrac{7}{3\cdot4}-\dfrac{9}{4\cdot5}+\dfrac{11}{5\cdot6}-\dfrac{13}{6\cdot7}+\dfrac{15}{7\cdot8}-\dfrac{17}{8\cdot9}+\dfrac{19}{9\cdot10}\\ =1-\left(\dfrac{5}{2}-\dfrac{5}{3}\right)+\left(\dfrac{7}{3}-\dfrac{7}{4}\right)-\left(\dfrac{9}{4}-\dfrac{9}{5}\right)+\left(\dfrac{11}{5}-\dfrac{11}{6}\right)-\left(\dfrac{13}{6}-\dfrac{13}{7}\right)+\left(\dfrac{15}{7}-\dfrac{15}{8}\right)-\left(\dfrac{17}{8}-\dfrac{17}{9}\right)+\left(\dfrac{19}{9}-\dfrac{19}{10}\right)\\ =1-\dfrac{5}{2}+\dfrac{5}{3}+\dfrac{7}{3}-\dfrac{7}{4}-\dfrac{9}{4}+\dfrac{9}{5}+\dfrac{11}{5}-\dfrac{11}{6}-\dfrac{13}{6}+\dfrac{13}{7}+\dfrac{15}{7}-\dfrac{15}{8}-\dfrac{17}{8}+\dfrac{17}{9}+\dfrac{19}{9}-\dfrac{19}{10}\\ =1-\dfrac{5}{2}+4-4+4-4+4-4+4-\dfrac{19}{10}\\ =1-\dfrac{5}{2}+4-\dfrac{19}{10}=\dfrac{3}{5}\)

Answer 2

[em bé pam xinh iu]

Giải thích các bước giải:

1−56+712−920+1130−1342+1556−1772+1990−21110+231321-56+712-920+1130-1342+1556-1772+1990-21110+23132

=16+215+235+263+299+2313216+215+235+263+299+23132

=310+445+796310+445+796

=710+796710+796

=0,58(3)