C = 1/(9.10) - 1/(8.9) - 1/(7.8) - ... - 1/(2.3) - 1/(1.2)
= 1/9 - 1/10 - 1/8 + 1/9 - 1/7 + 1/8 - ... - 1/2 + 1/3 - 1 + 1/2
= 1/9 - 1/10 + 1/9 - 1
= 2/9 - 11/10
= -79/90
Thực hiện phép tính:
\(A=3.\dfrac{1}{1.2}-5.\dfrac{1}{2.3}+7.\dfrac{1}{3.4}-...+15.\dfrac{1}{7.8}-17.\dfrac{1}{8.9}\)
Tính
M = 7.8+8.9+9.10+...+19.20
CMR: \(\dfrac{1}{2^2}+\dfrac{1}{3^2}+...+\dfrac{1}{20^2}< 1\)
Tính:
a) \(\dfrac{1}{1.2}\) + \(\dfrac{1}{2.3}\) + \(\dfrac{1}{3.4}\) +...+ \(\dfrac{1}{1999.2000}\)
b) \(\dfrac{1}{1.4}\) + \(\dfrac{1}{4.7}\) + \(\dfrac{1}{7.10}\) +...+ \(\dfrac{1}{100+103}\)
c) \(\dfrac{8}{9}\) - \(\dfrac{1}{72}\) - \(\dfrac{1}{56}\) - \(\dfrac{1}{42}\) -...-\(\dfrac{1}{6}\) - \(\dfrac{1}{2}\)
Tính tổng sau: \(A=\dfrac{1}{1.2}+\dfrac{1}{2.3}+\dfrac{1}{3.4}+...+\dfrac{1}{999.1000}\)
Tính: a) A=\(\dfrac{1}{2}\)+\(\dfrac{1}{2^2}\)+\(\dfrac{1}{2^3}\)+...+\(\dfrac{1}{2^{100}}\)
b) \(\dfrac{1}{1.2}\)+\(\dfrac{1}{2.3}\)+\(\dfrac{1}{3.4}\)+...+\(\dfrac{1}{2023.2024}\)
cứu tôi mng owiiii :((
\(x-\dfrac{1}{1.2}-\dfrac{1}{2.3}-\dfrac{1}{3.4}-...-\dfrac{1}{98.99}=\dfrac{1}{100}+\dfrac{1}{99.100}\)
\(\dfrac{8^{14}}{4^4.64^5}\)
\(\dfrac{9^{10}.27^7}{81^7.3^{15}}\)
\(\left(\dfrac{3}{10}\right)^4.\left(0,3\right)^5.\left(\dfrac{10}{3}\right)^{10}\)
\(\dfrac{\left(4^3\right)^2.9^4}{6^7.8^2}\)
\(\dfrac{4^8.9^4}{6^6.8^3}\)
\(3^6.\left(\dfrac{1}{3}\right)^6.81^2.\dfrac{1}{27^2}\) TÍNH
So sánh A và B với \(\dfrac{1}{2}\) biết :
\(A=\dfrac{1}{1.2^2}+\dfrac{1}{2.3^2}+\dfrac{1}{3.4^2}+........+\dfrac{1}{49.50^2}\) và
\(B=\dfrac{1}{2^2}+\dfrac{1}{3^2}+\dfrac{1}{4^2}+.......+\dfrac{1}{50^2}\)
Cho a,b,c thỏa mãn :
\(\dfrac{1}{a+b+c}=\dfrac{a+4b-c}{c}=\dfrac{b+4c-a}{a}=\dfrac{c+4a-b}{b}\)
Tính: \(P=\left(2+\dfrac{a}{b}\right)\left(3+\dfrac{b}{c}\right)\left(4+\dfrac{c}{a}\right)\)
Ai giải giúp mik với mik đag cần
