k mình nha

kết quả đúng là 36

Tìm x biết

(x+2)(12-2):4=25

Đặt $\left(\frac{1}{5}+\frac{1}{5^2}+\frac{1}{5^3}+...+\frac{1}{5^{100}}\right)=A$(15 +152 +153 +...+15100 )=A

ta có: $\left(\frac{1}{5}+\frac{1}{5^2}+\frac{1}{5^3}+...+\frac{1}{5^{100}}\right)=A$(15 +152 +153 +...+15100 )=A

5A=5$\left(\frac{1}{5}+\frac{1}{5^2}+\frac{1}{5^3}+...+\frac{1}{5^{100}}\right)$(15 +152 +153 +...+15100 )

5A=$1+\frac{1}{5}+\frac{1}{5^2}+..+\frac{1}{5^{101}}$1+15 +152 +..+15101 

5A-A=$\left(1+\frac{1}{5}+\frac{1}{5^2}+..+\frac{1}{5^{101}}\right)-$(1+15‍ +152 +..+15101 )−$\left(\frac{1}{5}+\frac{1}{5^2}+\frac{1}{5^3}+...+\frac{1}{5^{100}}\right)$(15 +152 +153 +...+15100 )

4A=1+$\frac{1}{5^{101}}$15101 

A=$\frac{1+\frac{1}{5^{101}}}{4}$1+15101 4 

ta có:

$\frac{1+\frac{1}{5^{101}}}{4}$1+15101 4 .x=1

$\Rightarrow x=\frac{1+\frac{1}{5^{101}}}{4}:1=\frac{1+\frac{1}{5^{101}}}{4}$⇒x=1+15101 4 :1=1+15101 4