Đáp án:
Giải thích các bước giải:
Bài 11:
a) 1/1.2 + 1/2.3 + 1/3.4+..........+ 1/ 2003.2004
=1/1 - 1/2 + 1/2 - 1/3 + 1/3- 1/4 +....+ 1/2003 - 1/2004
= 1/1 - 1/2004
=2004/ 2004 - 1/2004
=2003/2004
b) 1/1.3 + 1/ 3.5 + 1/5.8+............+ 1/ 2003. 2005
= 1/2 . ( 2/ 1.3 + 2/ 3.5+ 2/5.8 + .............+ 2/2003 .2005)
= 1/2 . ( 1/1 - 1/3 + 1/3 - 1/5 + 1/8+......+ 1/ 2003 - 1/2005)
=1/2. (1/1 - 1/2005)
=1/2 . (2005/2005 - 1/2005)
=1/2. 2004/2005
=2004/ 4010
= 1002/ 2005
Bài 10:
a) 3/4 - x = 1
x= 3/4 - 1
x= 3/4 - 4/4
x= -1/4
Vậy..........
b) x + 4 = 1/5
x= 1/5 -4
x= 1/5 -20/5
x= -19/5
Vậy.........
c) x - 1/5 = 2
x = 2+ 1/5
x = 10/5 + 1/5
x = 11/5
Vậy.............
d) x + 5/3 = 1/81
x = 1/81 - 5/3
x = 1/81 - 135/81
x = -134/81
Vậy..............
Bài 9:
a) 7/3 + 1/2 - 3/70
= 490/210 + 105/210 - 49/210
= 546/ 210
=13/5
b) 5/12 - 3/ -16 + 3/4
= 5/12 - -3/16 + 3/4
= 60/ 192 - -36/192 + 144/192
= 240/ 192
= 5/4
Bài 8: