900-1-3-5......-17-19
Hãy nhập câu hỏi của bạn vào đây, nếu là tài khoản VIP, bạn sẽ được ưu tiên trả lời.
a) \(\dfrac{\dfrac{3}{14}-\dfrac{3}{17}+\dfrac{3}{19}}{\dfrac{5}{19}+\dfrac{5}{14}-\dfrac{5}{17}}=\dfrac{3\left(\dfrac{1}{14}-\dfrac{1}{17}+\dfrac{1}{19}\right)}{5\left(\dfrac{1}{14}-\dfrac{1}{17}+\dfrac{1}{19}\right)}=\dfrac{3}{5}\)
c) \(\dfrac{\dfrac{2}{7}+\dfrac{2}{5}+\dfrac{2}{17}-\dfrac{2}{193}}{\dfrac{3}{7}+\dfrac{3}{5}+\dfrac{3}{17}-\dfrac{3}{293}}=\dfrac{2\left(\dfrac{1}{7}+\dfrac{1}{5}+\dfrac{1}{17}-\dfrac{1}{193}\right)}{3\left(\dfrac{1}{7}+\dfrac{1}{5}+\dfrac{1}{17}-\dfrac{1}{193}\right)}=\dfrac{2}{3}\)
d)
Đặt A = 1.3 + 3.5 + 5.7 + ... + 15.17 + 17.19
6A = 1.3.6 + 3.5.6 + .... + 15.17.6 + 17.19.6
6A = 1.3.(5 + 1) + 3.5.(7 - 1) + ... + 15.17.(19 - 13) + 17.19.(21 - 15)
6A = 1.3.5 + 1.3 + 3.5.7 - 1.3.5 + ... + 15.17.19 - 13.15.17 + 17.19.21 - 15.17.19
6A = (1.3.5 + 3.5.7 + ... + 15.17.19 + 17.19.21) - ( 1.3.5 + ... + 13.15.17 + 15.17.19) + 1.3
6A = 17.19.21 + 1.3
6A = 6783 + 3
6A = 6786
A = 6780 : 6 = 1131
chu so tan cung o ve phai la 0 vi co so 10 tan cung la 0. ve trai tan cung la 5 vi 5nhan so le nao cung tan cung la 5 vay chu so tan cung la 0-5 =5
\(\dfrac{4}{5}\)+\(\dfrac{-5}{4}\)=\(\dfrac{0}{4}\)
\(\dfrac{-1}{3}\)+\(\dfrac{2}{5}-\dfrac{5}{6}\)=\(\dfrac{-10}{30}+\dfrac{12}{30}-\dfrac{25}{30}\)=\(\dfrac{-23}{30}\)
\(\dfrac{2}{3}-\dfrac{5}{7}.\dfrac{14}{25}\)=\(\dfrac{2}{3}-\dfrac{2}{5}\)=\(\dfrac{10}{15}-\dfrac{6}{15}\)=\(\dfrac{4}{15}\)
800 nha bn
=900 - (1+3+5+...+17+19)
=900 - { (19+1)x [ (19-1):2+1 ] : 2}
=900 - ( 20 x 10 : 2 )
=900 - 100
=800
k nha