\(5^{x-1}+5^{x-2}+5^{x-3}=775\\ 5^{x-3}.\left(25+5+1\right)=775\\ 5^{x-3}.31=775\\ 5^{x-3}=\dfrac{775}{31}=25=5^2\\ x-3=2\\ x=5\)

Cảm ơn bn

\(5^x+5^{x+1}+5^{x+2}=775\)

\(\Leftrightarrow5^x.1+5^x.5+5^x.5^2=775\)

\(\Leftrightarrow5^x.\left(1+5+5^2\right)=775\)

\(\Leftrightarrow5^x.\left(1+5+25\right)=775\)

\(\Leftrightarrow5^x.31=775\)

\(\Rightarrow5^x=775:31=25=5^2\)

\(\Rightarrow x=2\)

Vậy \(x=2\)

5^x + 5^{x + 1} + 5^{x + 2} = 775

5^x . 1 + 5^x . 5 + 5^x . 25 = 775

5^x . (1 + 5 + 25) = 775

5^x . 31 = 775

5^x       = 775 : 31

5^x       = 25

5^x       = 5²

Suy ra : x = 2

      \(5^x+5^{x+1}+5^{x+2}=775\)

<=>\(5^x.\left(1+5+5^2\right)=775\)

<=>\(5^x.31=775\)

<=>\(5^x=775:31\)

<=>\(5^x=25\)=>\(x=2\)

dễ. k đi mình hứa sẽ làm cho

CÁC BẠN GIÚP MÌNH NHA

MAI MÌNH ĐI HỌC RỒI NHA

bài 2 tui ko làm đc 

A={245;250;255;260;....;770}

Tập hợp A có số p/tử là:

(770-245):5+1=106 p/tử

a,  22/105

b,  8/5

c,   10/21

a, \(-5x-1-\dfrac{x}{2}+\dfrac{1}{3}=\dfrac{3}{2}x-5\Leftrightarrow-7x=-\dfrac{13}{3}\Leftrightarrow x=\dfrac{13}{21}\)

b, \(3x-\dfrac{3}{2}-5x-3=-x+\dfrac{1}{5}\Leftrightarrow-x=\dfrac{47}{10}\Leftrightarrow x=-\dfrac{47}{10}\)

2:

a: =>x^2+3x-4x-12-(x^2-5x+x-5)=8

=>x^2-x-12-x^2+4x+5=8

=>3x-7=8

=>3x=15

=>x=5

b: =>3x^2+3x-2x-2-3x^2-21x=13

=>-20x=15

=>x=-3/4

c: =>x^2-25-x^2-2x=9

=>-2x=25+9=34

=>x=-17

d: =>x^3-1-x^3+3x=1

=>3x-1=1

=>3x=2

=>x=2/3