Tính nhanh : x x13,48 + x x 5,52 + x =40
K
Khách
Hãy nhập câu hỏi của bạn vào đây, nếu là tài khoản VIP, bạn sẽ được ưu tiên trả lời.
CM
2
19 tháng 2 2022
\(\dfrac{4}{3.5}+\dfrac{8}{5\cdot9}+\dfrac{12}{9\cdot15}+...+\dfrac{32}{n\left(n+6\right)}=\dfrac{16}{25}\)
\(2\left(\dfrac{1}{3}-\dfrac{1}{5}\right)+2\left(\dfrac{1}{5}-\dfrac{1}{9}\right)+2\left(\dfrac{1}{9}-\dfrac{1}{15}\right)+...+2\left(\dfrac{1}{n}-\dfrac{1}{n+16}\right)=\dfrac{16}{25}\)
\(2\left(\dfrac{1}{3}-\dfrac{1}{5}+\dfrac{1}{5}-\dfrac{1}{9}+\dfrac{1}{9}-\dfrac{1}{15}+...+\dfrac{1}{n}-\dfrac{1}{n+16}\right)=\dfrac{16}{25}\)
\(2\left(\dfrac{1}{3}-\dfrac{1}{n+16}\right)=\dfrac{16}{25}\)
\(\dfrac{1}{3}-\dfrac{1}{n+16}=\dfrac{8}{25}\)
\(\dfrac{1}{n+16}=\dfrac{1}{75}\)
⇒ \(n+16=75\)
\(\Rightarrow n=59\)
\(x.13,48+x.5,52+x=40\)
\(x.\left(13,48+5,52+1\right)=40\)
\(x.20=40\)
\(x=40:20\)
\(x=2\)
HT
\(x\times13,48+x\times5,52+x=40\)
\(x\times13,48+x\times5,52+x\times1=40\)
\(x\times\left(13,48+5,52+1\right)=40\)
\(x\times20=40\)
\(x=40:20\)
\(\Rightarrow x=2\)
Vậy x = 2
_HT_