tính nhanh
0.01+1.11+1.21+......+2.01
Những câu hỏi liên quan
cho a = 1/1.21 + 1/2.22+...+1/80.100 b= 1/1.81 + 1/2.82+...+1/20.100 tính a/b
Cho A=1/1.21+1/1.22+1/3.23+...+1/80.100
B=1/1.81+1/2.82+1/3.83+...+1/20.100
Tính A/B
A=20/1.21+20/2.22+...+20/80.100
=1-1/21+1/2-1/22+...+1/80-1/100
=(1+1/2+...+1/80)-(1/21+1/22+...+1/100)
80B=80/1.81+80/2.82+...+8/20.100
=1-1/81+1/2-1/82+...+1/20-1/100
=(1+1/2+...+1/20)-(1/81+1/82+...+1/100)
=(1+1/2+1/3+...+1/20+1/21+1/22+...+1/80)-(1/21+1/22+...1/80+1/81+1/82+...1/100)
=>20A=80B
=>A=4B
Đúng 1
Bình luận (0)
tính a/b biết a=1/1.21 + 1/2.22 + 1/3.23 + ... +1/80.100; b=1/1.81 + 1/2.82 + 1/3.82 + ... + 1/20.100
20a = 20/1.21 + 20/2.22+ ... + 20/80.100
= 1-1/21 + 1/2 - 1/22 +...+ 1/80 - 1/100
= 1 + 1/2 + 1/3 +... + 1/19 + 1/20 - 1/81 - 1/82 -.... - 1/100
80b = 80/1.81 + 80/2.82 + 80/3.83 +... + 80/20.100
= 1 - 1/81+ 1/2 - 1/83 +...+ 1/20 - 1/100
=> 20a = 80b
=> a/b = 4
Đúng 0
Bình luận (0)
18 tháng 4 2022 lúc 14:54
Câu 24 : Cho A = 1.21 + 1/2.22 + 1/3.23 + ... + 1/80.100 ; B = 1/1.81 + 1/2.82 + 1/3.83 + ... + 1/20.100 . Tính A/B
...1.21.
a) -3/7 + 5/13 + -4/7
= ( -3/7 + -4/7 ) + 5/13
= -7/7 +5/13
= -1 + 5/13
= -13/13 + 5/13
= -8/13
b) -5/21 + -2/21 + 8/24
= -7/21 + 8/24
= -1/3 + 1/3
= 0
Đúng 0
Bình luận (0)
a) \(\frac{-3}{7}+\frac{5}{13}+\frac{-4}{7}\)
\(=\left(\frac{-3}{7}+\frac{-4}{7}\right)+\frac{5}{13}\)
\(=\left(-1\right)+\frac{5}{13}\)
\(=-1\frac{5}{13}\)
b) \(\frac{-5}{21}+\frac{-2}{21}+\frac{8}{24}\)
\(=\left(\frac{-5}{21}+\frac{-2}{21}\right)+\frac{1}{3}\)
\(=\frac{-1}{3}+\frac{1}{3}\)
\(=0\)
Đúng 0
Bình luận (0)
Cho \(A=\dfrac{1}{1.21}+\dfrac{1}{2.22}+\dfrac{1}{3.23}+...+\dfrac{1}{80.100}\);
\(B=\dfrac{1}{1.81}+\dfrac{1}{2.82}+\dfrac{1}{3.83}+...+\dfrac{1}{20.100}\).
Tính \(\dfrac{A}{B}\).
A=20/1.21+20/2.22+...+20/80.100
=1-1/21+1/2-1/22+...+1/80-1/100
=(1+1/2+...+1/80)-(1/21+1/22+...+1/100)
80B=80/1.81+80/2.82+...+8/20.100
=1-1/81+1/2-1/82+...+1/20-1/100
=(1+1/2+...+1/20)-(1/81+1/82+...+1/100)
=(1+1/2+1/3+...+1/20+1/21+1/22+...+1/80)-(1/21+1/22+...1/80+1/81+1/82+...1/100)
=>20A=80B
=>A=4B
Đúng 3
Bình luận (0)
số nào nhân với chính no bằng 1.21
Xem thêm câu trả lời
tính nhanh:
1.1-1.11+1.12-1.13...-1.97+1.98=
Đặt \(A=1.1-1.11+1.12-1.13+...-1.97+1.98=0.1-0.11+0.12-0.13+...-0.97+1.98\)
\(100A=10-11+12-13+...+96-97+198=198-44=154\Rightarrow A=1.54\)
Đúng 0
Bình luận (0)
18 tháng 4 2022 lúc 14:51
Câu 24 : Cho A = 1/1.21 + 1/2.22 + 1/3.23 + ...+ 1/80.10