Bài 1

Cho phân số a/b khác 1 . Tìm phân số c/d sao cho a/b + c/d = a/b . c/d

aaa:a

abab: ab

abc abc:abc

X-40%=36

tính

\(G=\left(1-\dfrac{1}{7}\right)\left(1-\dfrac{2}{7}\right)\left(1-\dfrac{3}{7}\right)...\left(1-1\dfrac{2}{7}\right)\left(1-1\dfrac{3}{7}\right)\)

1. E = \(\dfrac{3}{1.4}+\dfrac{3}{4.7}+\dfrac{3}{7.10}+\dfrac{3}{10.13}+\dfrac{3}{13.16}+\dfrac{3}{16.19}+\dfrac{3}{19.22}\)

2. (x-4)(x-5)=0

30%x+x=52

Tìm x biết :

\(\dfrac{1}{2.4}+\dfrac{1}{4.6}+...+\dfrac{1}{\left(2x-2\right)2x}=\dfrac{1}{8}\left(x\in N,x\ge2\right)\)

Chứng minh

\(\dfrac{1}{2}\) + \(\dfrac{1}{2^2}\) + ... + \(\dfrac{1}{2^{30}}\) < 1

tính

\(F=\left(1-\dfrac{1}{5}\right).\left(1-\dfrac{1}{6}\right).\left(1-\dfrac{1}{7}\right)...\left(1-\dfrac{1}{100}\right)\)

cmr \(\dfrac{1}{6}< \dfrac{1}{5^2}+\dfrac{1}{6^2}+\dfrac{1}{7^2}+...+\dfrac{1}{100^2}< \dfrac{1}{4}\)