Tính:
A=1/2.9 + 1/9.7 + 1/7.19 + ... + 1/252.509
B=5/1.4 + 29/4.7 + 71/7.10 + 10301/100.103
Những câu hỏi liên quan
Tính:
\(A=\frac{5}{1.4}+\frac{29}{4.7}+\frac{71}{7.10}+...+\frac{10301}{100.103}\)
Tính :
a)A=1/2.9 + 1/9.7 + 1/7.19 + ...+1/252.509
b)B=1/10.9 + 1/18.13 + 1/26.17 + ... + 1/802.405
c)C=2/4.7 - 3/5.9 +2/7.10 - 3/9.13+...+2/301.304 - 3/401.405
\(A=\frac{1}{2.9}+\frac{1}{9.7}+...+\frac{1}{252.509}\)
\(A=\frac{2}{4.9}+\frac{2}{9.14}+...+\frac{2}{504.509}\)
\(A=\frac{2}{5}.\left(\frac{5}{4.9}+\frac{5}{9.14}+...+\frac{5}{504.509}\right)\)
\(A=\frac{2}{5}.\left(\frac{9-4}{4.9}+\frac{14.9}{9.14}+...+\frac{509-504}{504.509}\right)\)
\(A=\frac{2}{5}.\left(\frac{1}{4}-\frac{1}{9}+\frac{1}{9}-\frac{1}{14}+...+\frac{1}{504}-\frac{1}{509}\right)\)
\(A=\frac{2}{5}.\left(\frac{1}{4}-\frac{1}{509}\right)\)
\(A=\frac{2}{5}.\frac{505}{2036}\)
\(A=\frac{101}{1018}\)
\(B=\frac{1}{10.9}+\frac{1}{18.13}+\frac{1}{26.17}+...+\frac{1}{802.405}\)
\(\frac{1}{2}B=\frac{1}{10.9.2}+\frac{1}{18.13}+\frac{1}{26.17}+...+\frac{1}{802.405.2}\)
\(\frac{1}{2}B=\frac{1}{10.18}+\frac{1}{18.26}+\frac{1}{26.34}+...+\frac{1}{802.810}\)
\(4B=\frac{8}{10.18}+\frac{8}{18.26}+\frac{8}{26.34}+...+\frac{8}{802.810}\)
\(4B=\frac{18-10}{10.18}+\frac{26-18}{28.26}+\frac{34-26}{26.34}+...+\frac{810-802}{802.810}\)
\(4B=\frac{1}{10}-\frac{1}{18}+\frac{1}{18}-\frac{1}{26}+\frac{1}{26}-\frac{1}{34}+...+\frac{1}{802}-\frac{1}{810}\)
\(4B=\frac{1}{10}-\frac{1}{810}\)
\(4B=\frac{8}{81}\)
\(B=\frac{2}{81}\)
\(C=\frac{2}{4.7}-\frac{3}{5.9}+\frac{2}{7.10}-\frac{3}{9.13}+...+\frac{2}{301.304}-\frac{3}{401.405}\)
\(C=\left(\frac{2}{4.7}+\frac{2}{7.10}+...+\frac{2}{301.304}\right)-\left(\frac{3}{5.9}+\frac{3}{9.13}+...+\frac{3}{401.405}\right)\)
\(C=\frac{2}{3}.\left(\frac{1}{4}-\frac{1}{7}+\frac{1}{7}-\frac{1}{10}+...+\frac{1}{301}-\frac{1}{304}\right)-\frac{3}{4}.\left(\frac{1}{5}-\frac{1}{9}+\frac{1}{9}-\frac{1}{13}+...+\frac{1}{401}-\frac{1}{405}\right)\)
\(C=\frac{2}{3}.\left(\frac{1}{4}-\frac{1}{304}\right)-\frac{3}{4}.\left(\frac{1}{5}-\frac{1}{405}\right)\)
\(C=\frac{2}{3}.\frac{75}{304}-\frac{3}{4}.\frac{16}{81}\)
\(C=\frac{25}{152}-\frac{4}{27}\)
\(C=\frac{67}{4104}\)
1/2.9+1/9.7+1/7.19+..........+1/252.509 = ?
Sử dụng điều kiện \(\dfrac{n}{a\left(a+n\right)}=\dfrac{1}{a}-\dfrac{1}{a+n}\) để tính:
a. \(A=\dfrac{1}{2.9}+\dfrac{1}{9.7}+\dfrac{1}{7.19}+...+\dfrac{1}{252.509}\)
b.\(B=\dfrac{2}{4.7}-\dfrac{3}{5.9}+\dfrac{2}{7.10}-\dfrac{3}{9.13}+...+\dfrac{2}{301.304}-\dfrac{3}{401.405}\)
A=1/2.9+1/9.7+1/7.19+...+1/252.509
=?
??????
Tính A:
\(\frac{1}{2.9}+\frac{1}{9.7}+\frac{1}{7.19}+...+\frac{1}{252.509}\)
Đặt \(A=\frac{1}{2.9}+\frac{1}{9.7}+\frac{1}{7.19}+...+\frac{1}{252.509}\)
\(\Leftrightarrow A=\frac{2}{5}.\left(\frac{5}{4.9}+\frac{5}{9.14}+\frac{5}{14.19}+...+\frac{5}{504.509}\right)\)
\(\Leftrightarrow A=\frac{2}{5}.\left(\frac{1}{4}-\frac{1}{9}+\frac{1}{9}-\frac{1}{14}+\frac{1}{14}-\frac{1}{19}+...+\frac{1}{504}-\frac{1}{509}\right)\)
\(\Leftrightarrow A=\frac{2}{5}.\left(\frac{1}{4}-\frac{1}{509}\right)\)
\(\Leftrightarrow A=\frac{2}{5}.\frac{505}{2036}\)
\(\Leftrightarrow A=\frac{101}{1018}\)
~ Hok tốt ~
Đúng 0
Bình luận (0)
#)Giải :
\(A=\frac{1}{2.9}+\frac{1}{9.7}+\frac{1}{7.19}+...+\frac{1}{252.509}\)
\(A=\frac{2}{5}\left(\frac{5}{4.9}+\frac{5}{9.14}+\frac{5}{14.19}+...+\frac{5}{504.509}\right)\)
\(A=\frac{2}{5}\left(\frac{1}{4}-\frac{1}{9}+\frac{1}{9}-\frac{1}{14}+\frac{1}{14}-\frac{1}{17}+...+\frac{1}{504}-\frac{1}{509}\right)\)
\(A=\frac{2}{5}\left(\frac{1}{4}-\frac{1}{509}\right)\)
\(A=\frac{2}{5}\times\frac{505}{2036}\)
\(A=\frac{101}{1018}\)
Đúng 0
Bình luận (0)
Tính
a) A= 1/2.9 + 1/9.7 + 1/7.19 +....+ 1/252.509
b) B= 1/10.9 + 1/18.13 + 1/26.17+.... + 1/802.405
Nhanh nhaaa iuuu
a)Ta có:
A= 1/2.9 + 1/9.7 +...+1/252.509
= 2/5.(5/4.9 + 5/9.14 + 5/14.19 +...+ 1/504.509)
= 2/5.(1/4 - 1/9 + 1/9 - 1/14 + 1/14 - 1/19 +...+ 1/504 - 1/509)
= 2/5.(1/4 - 1/509)
= 101/1018
Vậy A = 101/1018
b)Ta có:
B= 1/10.9 +1/18.13 + 1/26.17 +...+ 1/802.405)
= 1/4.(8/10.18 + 8/18.26 + 8/26.34 +...+ 8/802.810)
= 1/4.(1/10 - 1/18 + 1/18 - 1/26 + 1/26 - 1/34 +...+ 1/802 - 1/810)
= 1/4.(1/10 - 1/810)
= 2/81
Vậy B= 2/81
Tk mình nha!!!
Đúng 0
Bình luận (0)
Xem thêm câu trả lời
*Tính:
a) A = \(\frac{1}{2.9}+\frac{1}{9.7}+\frac{1}{7.19}+...+\frac{1}{252.509}\)
b) B = \(\frac{1}{10.9}+\frac{1}{18.13}+\frac{1}{26.17}+...+\frac{1}{802.405}\)
c) C = \(\frac{2}{4.7}-\frac{3}{5.9}+\frac{2}{7.10}-\frac{3}{9.13}+...+\frac{2}{301.304}-\frac{3}{401.405}\)
Giải giúp mình, mình đang gấp
a)b) Bạn nhân cả tử và mẫu với 2. Mình làm luôn, ko ghi lại đề bài
a)\(\frac{2}{4.9}+\frac{2}{9.14}+\frac{2}{14.19}+...+\frac{2}{504.509}\)
=\(\frac{2}{5}.\left(\frac{1}{4}-\frac{1}{9}+\frac{1}{9}-\frac{1}{14}+\frac{1}{14}-\frac{1}{19}+...+\frac{1}{504}-\frac{1}{509}\right)\)
=\(\frac{2}{5}.\left(\frac{1}{4}-\frac{1}{509}\right)\)
=\(\frac{2}{5}.\frac{505}{2036}=\frac{101}{1018}\)
b)\(\frac{2}{10.18}+\frac{2}{18.26}+\frac{2}{26.34}+...+\frac{2}{802.810}\)
=\(\frac{1}{4}\left(\frac{1}{10}-\frac{1}{18}+\frac{1}{18}-\frac{1}{26}+\frac{1}{26}-\frac{1}{34}+...+\frac{1}{802}-\frac{1}{810}\right)\)
=\(\frac{1}{4}.\left(\frac{1}{10}-\frac{1}{810}\right)\)
=\(\frac{1}{4}.\frac{8}{81}=\frac{2}{81}\)
c) Mình biết làm, ddoiwtj tí nữa mình làm cho. Giờ đang mỏi tay
Thẳng Nobita kun có chép bài thì đừng t..i..c..k cho nó
Đúng 0
Bình luận (0)
Xem thêm câu trả lời
Tính:
A=\(\frac{1}{2.9}+\frac{1}{9.7}+\frac{1}{7.19}+...+\frac{1}{252.509}\)
B=\(\frac{1}{10.9}+\frac{1}{18.13}+\frac{1}{26.17}+...+\frac{1}{802.405}\)
C=\(\frac{2}{4.7}-\frac{3}{5.9}+\frac{2}{7.10}-\frac{3}{9.13}+...+\frac{2}{301.304}-\frac{3}{401.405}\)
Giúp mik nhá mọi người. THANKS NHÌU............................................................
A=\(\frac{1}{2.9}+\frac{1}{9.7}+\frac{1}{7.19}+...+\frac{1}{252.509}\)
=\(\frac{1}{2}-\frac{1}{509}\)
=\(\frac{507}{1018}\)
Đúng 0
Bình luận (0)
so sánh A VỚI 1/10
A=1/2.9 + 1/9.7 + 1/7.19 + ... + 1/252.509
