Đáp án:
Giải thích các bước giải:
Bài 2
a)A=1-1/2+1/2-1/3+...+1/2019-1/2020
=1-1/2020
=2019/2020
b)B=2/3.(2/1.3+2/3.5+...+2/199.201)
=2/3.(1-1/3+1/3-1/5+...+1/199-1/201)
=2/3.(1-1/201)
=2/3.200/201
=400/603
Bài1
a)=-3/7+3/7+5/13
=0+5/13
=5/13
b)=-1/3+1/3
=0
c)=-5/11+(-6/11)+2
=-1+2
=1
d)=-1/32+1/2+(-15/32)
=-1/2+1/2
=0
e)=-9/17.-1+-9/17.3/14+-9/17.11/14
=-9/17.(-1+3/14+11/14)
=-9/17.0
=0
f)=5/9.(10/11+14/11-15/11)
=5/9.9/11
=5/11
g)=(-5/19+-14/19).8/19-11/19
=-1.8/19-11/19
=-8/19-11/19
=-1
h)=3/19.(7/5-2/5)-1
=3/19.1-1
=3/19-1
=-16/19