Bài này không khó lắm bn hãy nhìn cách làm của mk nhé!
B=\(\dfrac{2.4.10+4.6.8+14.16.18}{3.6.15+6.9.12+21.24.30}\)= \(\dfrac{2\left(1.2.5+2.3.4+7.8.10\right)}{3\left(1.2.5+2.3.4+7.8.10\right)}\)
= \(\dfrac{2}{3}\)
Vậy B=\(\dfrac{2}{3}\)
Nếu bn nghĩ là đúng hãy tick cho mk nha!
Chúc bn học tốt!!!
B = \(\dfrac{\text{2.4.10+4.6.8+14.16.20}}{3.6.15+6.9.12+21.24.30}\)
Cho A =4/2.4.6 +4/4.6.8+4/6.8.10+.......+4/46.48.50 tìm số nghịch đảo của A
Chứng minh rằng:
1) B =\(\dfrac{1}{4}+\dfrac{1}{5}+\dfrac{1}{6}+...+\dfrac{1}{19}>1\)
2) \(A=\dfrac{1}{5}+\dfrac{2}{5^2}+\dfrac{3}{5^3}+\dfrac{4}{5^4}+...+\dfrac{500}{5^{500}}<100\)
3) \(C=\dfrac{1}{2^3}+\dfrac{1}{3^3}+\dfrac{1}{4^3}+\dfrac{1}{5^3}+...+\dfrac{1}{500^3}<\dfrac{1}{4}\)
4) \(D=\dfrac{4}{3}+\dfrac{10}{9}+\dfrac{28}{27}+...+\dfrac{3^{98}+1}{3^{98}}<100\)
Làm giúp mình sớm nha! Thanks.
Giúp mình với :
1.Tính
a, \(\dfrac{9}{5}-\dfrac{5}{9}\)
b, \(\dfrac{7}{2}+\dfrac{4}{5}+\dfrac{3}{6}\)
c, \(\left(\dfrac{5}{6}-\dfrac{4}{24}\right)+\dfrac{1}{3}\)
d,\(\left(\dfrac{9}{12}-\dfrac{10}{20}\right)-\dfrac{1}{8}\)
Bài 1: Tính
\(\dfrac{A}{B}=\dfrac{\dfrac{1}{2}+\dfrac{1}{3}+\dfrac{1}{4}+...+\dfrac{1}{309}}{\dfrac{308}{1}+\dfrac{307}{2}+\dfrac{306}{3}+...+\dfrac{1}{308}}\)
BÀi 2: Cho S = \(\dfrac{1}{101}+\dfrac{1}{102}+...+\dfrac{1}{130}\)
Chứng minh \(\dfrac{1}{4}< S< \dfrac{91}{330}\)
cho \(\dfrac{a}{b}=\dfrac{c}{d}\)
Chứng tỏ \(\dfrac{a+b}{b}=\dfrac{c+d}{d};\dfrac{a-b}{b}=\dfrac{c-d}{d}\)
Bài 1 : Cho \(\dfrac{a}{b}=\dfrac{c}{d}\). Chứng Minh :
a) \(\dfrac{2a+c}{2b+d}=\dfrac{a-c}{b-d}\)
b) \(\dfrac{a^2}{b^2}=\dfrac{ac+c^2}{bd+d^2}\)
c) \(\dfrac{a+3c}{b+3d}=\dfrac{a-c}{b-d}\)
d) \(\dfrac{2a-3c}{2b-3d}=\dfrac{a}{b}\)
e) \(\dfrac{a+3b}{c+3d}=\dfrac{b}{d}\)
Bài 1:Tính
a, A=\(\dfrac{3}{4}\cdot\dfrac{8}{9}\cdot\dfrac{15}{16}\cdot....\cdot\dfrac{9999}{10000}\)
b,B=\(\left(1-\dfrac{1}{21}\right)\cdot\left(1-\dfrac{1}{28}\right)\cdot\left(1-\dfrac{1}{36}\right)\cdot....\cdot\left(1-\dfrac{1}{1326}\right)\)
c,C=\(\left(1+\dfrac{1}{1\cdot3}\right)\cdot\left(1+\dfrac{1}{2\cdot4}\right)\cdot\left(1+\dfrac{1}{3\cdot5}\right)\cdot....\cdot\left(1+\dfrac{1}{99\cdot101}\right)\)
Tính nhanh : \(\dfrac{1}{1}.\dfrac{1}{2}+\dfrac{1}{2}.\dfrac{1}{3}+\dfrac{1}{3}.\dfrac{1}{4}+...+\dfrac{1}{998}.\dfrac{1}{999}+\dfrac{1}{999}.\dfrac{1}{1000}\)