\(\left(\frac{1}{7}x-\frac{2}{7}\right)\left(\frac{1}{5}x+\frac{3}{5}\right)\left(\frac{1}{3}x+\frac{4}{3}\right)=0\)

<=> \(\frac{x-2}{7}.\frac{x+3}{5}.\frac{x+4}{3}=0\)

<=> \(\frac{x-2}{7}=0\)hoặc \(\frac{x+3}{5}=0\); \(\frac{x+4}{3}=0\)

Nếu \(\frac{x-2}{7}=0\)<=> \(x-2=0\)<=> \(x=2\)
Nếu \(\frac{x+3}{5}=0\)<=> \(x+3=0\) <=> \(x=3\)

Nếu \(\frac{x+4}{3}=0\)<=> \(x+4=0\)<=> \(x=4\)

Vây x= 2 hoặc 3; 4

khó quá nhiw

\(B=1+\frac{1}{5}+\frac{1}{5^2}+\frac{1}{5^3}+...+\frac{1}{5^{100}}\)

\(\Rightarrow5B=5+1+\frac{1}{5}+\frac{1}{5^2}+...+\frac{1}{5^{99}}\)

\(\Rightarrow5B-B=5-\frac{1}{5^{100}}\)

\(\Rightarrow B=\frac{5-\frac{1}{5^{100}}}{4}\)

\(B=1+\frac{1}{5}+\frac{1}{5^2}+\frac{1}{5^3}+...+\frac{1}{5^{100}}\)

\(5B=1+5+\frac{1}{5}+\frac{1}{5^2}+...+\frac{1}{5^{99}}\)

\(5B-B=\left(1+5+\frac{1}{5}+...+\frac{1}{5^{99}}\right)-\left(1+\frac{1}{5}+\frac{1}{5^2}+...+\frac{1}{5^{100}}\right)\)

\(4B=5-\frac{1}{5^{100}}\)

\(B=\frac{5-\frac{1}{5^{100}}}{4}\)

hok tốt!!

Trả lời:

\(B=1+\frac{1}{5}+\frac{1}{5^2}+\frac{1}{5^3}+...+\frac{1}{5^{100}}\)

\(\Rightarrow5B=5+1+\frac{1}{5}+...+\frac{1}{5^{99}}\)

\(\Rightarrow5B-B=\left(5+1+\frac{1}{5}+...+\frac{1}{5^{99}}\right)\left(1+\frac{1}{5}+\frac{1}{5^2}+...+\frac{1}{5^{100}}\right)\)

\(\Leftrightarrow4B=5+1+\frac{1}{5}+...+\frac{1}{5^{99}}+1-\frac{1}{5}-\frac{1}{5^2}-...-\frac{1}{5^{100}}\)

\(\Leftrightarrow\frac{4}{5}B=\left(5-\frac{1}{5^{100}}\right)+\left(1-1\right)+...+\left(\frac{1}{5^{99}}-\frac{1}{5^{99}}\right)\)

\(\Leftrightarrow4B=5-\frac{1}{5^{100}}+0+...+0\)

\(\Leftrightarrow4B=5-\frac{1}{5^{100}}\)

\(\Leftrightarrow B=\left(5-\frac{1}{5^{100}}\right):4\)

Vậy\(B=\frac{5-\frac{1}{5^{100}}}{4}\)

P/s: Bài còn sai sót gì thì mong các bạn thông cảm và chỉ ra lỗi sai.

Hok tốt!

Good girl

       \(\frac{2}{5}\times\frac{1}{2}-\frac{2}{5}\times\frac{1}{3}-\frac{2}{5}\times\)\(\frac{1}{6}\)

\(=\frac{2}{5}\times\left(\frac{1}{2}-\frac{1}{3}-\frac{1}{6}\right)\)

\(=\frac{2}{5}\times\frac{0}{6}\)

\(=\frac{2}{5}\times0\)

\(=0\)

\(\frac{2}{5}\times\frac{1}{2}-\frac{2}{5}\times\frac{1}{3}-\frac{2}{5}\times\frac{1}{6}\)

\(=\frac{2}{5}\times\left(\frac{1}{2}-\frac{1}{3}-\frac{1}{6}\right)\)

\(=\frac{2}{5}\times0\)

\(=0\)

\(\frac{2}{5}\times\frac{1}{2}-\frac{2}{5}\times\frac{1}{3}-\frac{2}{5}\times\frac{1}{6}\)

\(=\frac{2}{5}\times\left(\frac{1}{2}-\frac{1}{3}-\frac{1}{6}\right)\)

\(=\frac{2}{5}\times\left(\frac{3}{6}-\frac{2}{6}-\frac{1}{6}\right)\)

\(=\frac{2}{5}\times0\)

\(=0\)

Học tốt

a) A= 3.(x²-2xy+y²)- 2. (x²+2xy+y²) - x²-y²

A= 3.x²-2xy+y²-2. x²+2xy+y²-x²-y²

`a)5/9:(1/11-5/22)+5/9:(1/15-2/3)`

`=5/9:(2/22-5/22)+5/9:(1/15-10/15)`

`=5/9:(-3)/22+5/9:(-9)/15`

`=5/9*(-22)/3+5/9*(-5)/3`

`=5/9*(-22/3+(-5)/3)`

`=5/9*(-9)=-5`

Bài làm

\(4\frac{1}{5}-\left(2\frac{3}{7}+8\frac{1}{5}\right)\)

\(=\frac{21}{5}-\left(\frac{17}{7}+\frac{41}{5}\right)\)

\(=\frac{147}{35}-\left(\frac{85}{35}+\frac{287}{35}\right)\)

\(=\frac{147-85-287}{35}=\frac{-225}{35}=-\frac{45}{7}\)

Đáp số là - \(\frac{45}{7}\)

Ok chúc bn học giỏi nha

Đặt \(\left(1+5+5^2+5^3+...+5^{2010}+5^{2011}\right)\) là A

\(\Rightarrow5A=5+5^2+5^3+5^4+...+5^{2011}+5^{2012}\)

\(\Rightarrow5A-A=5+5^2+5^3+5^4+...+5^{2011}+5^{2012}-1-5-5^2-5^3-...-5^{2010}-5^{2011}\)

\(\Rightarrow4A=5^{2012}-1\)

\(\Rightarrow A=\frac{1}{4}\left(5^{2012}-1\right)\)

Thay A vào, ta có:

\(\frac{1}{4}\left(5^{2012}-1\right)\left(x-1\right)=5^{2012}-1\)

\(\frac{1}{4}\left(x-1\right)=1\)

\(x-1=4\)

\(x=3\)