Tính
4/12 + 4/20 + 4/30 +... + 4/306
K
Khách
Hãy nhập câu hỏi của bạn vào đây, nếu là tài khoản VIP, bạn sẽ được ưu tiên trả lời.
Những câu hỏi liên quan
30 tháng 3 2018
Đặt \(A=\frac{4}{12}+\frac{4}{20}+\frac{4}{30}+...+\frac{4}{306}\)
\(=4.\left(\frac{1}{12}+\frac{1}{20}+\frac{1}{30}+...+\frac{1}{306}\right)\)
\(=4.\left(\frac{1}{3.4}+\frac{1}{4.5}+\frac{1}{5.6}+...+\frac{1}{17.18}\right)\)
\(=4.\left(\frac{1}{3}-\frac{1}{4}+\frac{1}{4}-\frac{1}{5}+...+\frac{1}{17}-\frac{1}{18}\right)\)
\(=4.\left(\frac{1}{3}-\frac{1}{18}\right)\)
\(=4.\frac{5}{18}=\frac{10}{9}\)
Vậy A=\(\frac{10}{9}\)
30 tháng 3 2018
\(\frac{4}{12}+\frac{4}{20}+\frac{4}{30}+.......+\frac{4}{306}\)
\(=\frac{4}{3.4}+\frac{4}{4.5}+\frac{4}{5.6}+.....+\frac{4}{17.18}\)
\(=4\left(\frac{1}{3.4}+\frac{1}{4.5}+\frac{1}{5.6}+.......+\frac{1}{17.18}\right)\)
\(=4\left(\frac{1}{3}-\frac{1}{4}+\frac{1}{4}-\frac{1}{5}+\frac{1}{5}-\frac{1}{6}+......+\frac{1}{17}-\frac{1}{18}\right)\)
\(=4\left(\frac{1}{3}-\frac{1}{18}\right)\)
\(=4.\frac{5}{18}\)
\(=\frac{10}{9}\)
DC
16 tháng 4 2022
BT1 :thực hành phép tính
4/3+-11/31+3/10-20/31-2/5 = 7/30
7/12-1/-16+3/4 = 67/48
2/11.-5/4+-9/11.5/4+ 1 và 3/4 = -1/4 * và 3/4 là sao bạn *
-9/27-25/75 = -2/3
30 tháng 3 2018
Bài 1:
\(\frac{4}{12}+\frac{4}{20}+\frac{4}{30}+...+\frac{4}{306}\)
\(=4\cdot\left(\frac{1}{12}+\frac{1}{20}+\frac{1}{30}+...+\frac{1}{306}\right)\)
\(=4\cdot\left(\frac{1}{3\cdot4}+\frac{1}{4\cdot5}+\frac{1}{5\cdot6}+...+\frac{1}{17\cdot18}\right)\)
\(=4\cdot\left(\frac{1}{3}-\frac{1}{4}+\frac{1}{4}-\frac{1}{5}+\frac{1}{5}-\frac{1}{6}+...+\frac{1}{17}-\frac{1}{18}\right)\)
\(=4\cdot\left(\frac{1}{3}-\frac{1}{18}\right)\)
\(=4\cdot\left(\frac{6}{18}-\frac{1}{18}\right)\)
\(=4\cdot\frac{5}{18}\)
\(=\frac{10}{9}\)
Bài 2 :
\(\left(3x-4\right)-\left(6x+7\right)=8\)
\(3x-4-6x-7=8\)
\(\left(3x-6x\right)-\left(4+7\right)=8\)
\(-3x-11=8\)
\(-3x=8+11\)
\(-3x=19\)
\(x=19:\left(-3\right)\)
\(x=\frac{-19}{3}\)
Vậy \(x=\frac{-19}{3}\)
b ) \(\left(\frac{4}{5}x+3\right):\left(-4\right)=\frac{1}{2}\)
\(\frac{4}{5}x+3=\frac{1}{2}\cdot\left(-4\right)\)
\(\frac{4}{5}x+3=-2\)
\(\frac{4}{5}x=\left(-2\right)-3\)
\(\frac{4}{5}x=-5\)
\(x=\left(-5\right):\frac{4}{5}\)
\(x=\left(-5\right)\cdot\frac{4}{5}\)
\(x=-4\)
Vậy \(x=-4\)
k nha !
30 tháng 3 2018
\(\frac{4}{12}\)+\(\frac{4}{20}\)+...+\(\frac{4}{306}\)=\(\frac{4}{3.4}\)+\(\frac{4}{4.5}\)+...+\(\frac{4}{17.18}\)=4(\(\frac{1}{3}\)-\(\frac{1}{4}\)+\(\frac{1}{4}\)-\(\frac{1}{5}\)+...+\(\frac{1}{17}\)-\(\frac{1}{18}\))
=4(\(\frac{1}{3}\)-\(\frac{1}{8}\))=4.\(\frac{5}{24}\)=\(\frac{5}{6}\)
16 tháng 4 2022
Bài 2:
a: 5/7-3/7x=1
=>3/7x=-2/7
hay x=-2/3
b: \(x+\dfrac{2}{3}=\dfrac{-1}{12}\cdot\dfrac{-4}{5}=\dfrac{1}{15}\)
=>x=1/15-2/3=-9/15=-3/5
c: \(x-4=\dfrac{-14}{35}:\dfrac{7}{5}=\dfrac{-14}{35}\cdot\dfrac{5}{7}=\dfrac{-70}{245}=\dfrac{-2}{7}\)
=>x=4-2/7=26/7
TT
1
1 tháng 3 2022
a: =5/4-3/4=2/4=1/2
b: =30/45-18/45=12/45=4/15
c: =10/12-9/12=1/12
d: =4/3-1/4=16/12-3/12=13/12
Đặt \(A=\frac{4}{12}+\frac{4}{20}+\frac{4}{30}+...+\frac{4}{306}\)
\(\Rightarrow A=4\left(\frac{1}{12}+\frac{1}{20}+\frac{1}{30}+...+\frac{1}{306}\right)\)
\(\Rightarrow A=4\left(\frac{1}{3}-\frac{1}{4}+\frac{1}{4}-\frac{1}{5}+\frac{1}{5}-\frac{1}{6}+...+\frac{1}{17}-\frac{1}{18}\right)\)
\(\Rightarrow A=4\left(\frac{1}{3}-\frac{1}{18}\right)\)
\(\Rightarrow A=4.\frac{5}{18}\)
\(\Rightarrow A=\frac{10}{9}\)
Đặt A= \(\frac{4}{12}+\frac{4}{20}+\frac{4}{30}+....+\frac{4}{306}\)
\(=4\left(\frac{1}{12}+\frac{1}{20}+\frac{1}{30}+...+\frac{1}{306}\right)\)
\(=4\left(\frac{1}{3.4}+\frac{1}{3.5}+\frac{1}{5.6}+......+\frac{1}{17.18}\right)\)
\(=4\left(\frac{1}{3}-\frac{1}{4}+\frac{1}{4}-\frac{1}{5}+....+\frac{1}{17}-\frac{1}{18}\right)\)
\(=4.\left(\frac{1}{3}-\frac{1}{18}\right)\)
Vậy A = \(\frac{10}{9}\)