(7x-11)³=(-3)³.15+208

(7x-11)³=-27.15+208

(7x-11)³=-405+208

(7x-11)³=-197

Vô lí vì -197 ko chuyển sang mũ 3 đc.

Vậy \(x\in\varnothing\)

Tao ghét mây đứa tên trâm

( 7x - 11 )^3 = ( -3 ) ^2 x 15 + 208

( 7x - 11 )^3 =      9 x 15 + 208

( 7x - 11 )^3 =     135 + 208 

( 7x - 11 )^3 =          343 

( 7x - 11)^3  =      7^3 

7x - 11 = 7 

7x       = 18

  x       = 18/7

(7x-11)³=(-3)²x15+208

(7x-11)³=9x15+208

(7x-11)³=135+208

(7x-11)³=343

(7x-11)³=7³

7x-11=7

7x=7+11

7x=18

x=18 : 7

x=18/7

(7x-11)^3=9x15+208=135+208=343=7^3

7x-11=7

x=11+7:7

x=18/7

mình sửa lại nha, nãy mình nhìn nhầm dấu:

343x³ - 1617x² + 2541x - 1674 = 0

x = 18/7 là nghiệm duy nhất của phương trình đã cho

a)

 \(\left(2x-15\right)^5=\left(2x-15\right)^3\\ \Leftrightarrow\left(2x-15\right)^5-\left(2x-15\right)^3=0\\ \Leftrightarrow\left(2x-15\right)^3.\left[\left(2x-15\right)^2-1\right]=0\\ \Leftrightarrow\left[{}\begin{matrix}2x-15=0\\\left(2x-15\right)^2-1=0\end{matrix}\right.\\ \Leftrightarrow\left[{}\begin{matrix}2x-15=0\\\left(2x-15-1\right).\left(2d-15+1\right)=0\end{matrix}\right.\\\Leftrightarrow\left[{}\begin{matrix}2x-15=0\\2x-16=0\\2x-14=0\end{matrix}\right.\Leftrightarrow\left[{}\begin{matrix}x=\dfrac{15}{2}\\x=8\\x=7\end{matrix}\right. \)

b) \(\left(7x-11\right)^3=\left(-3\right)^2.15+208\\ \Leftrightarrow\left(7x-11\right)^3=343=7^3\\ \Leftrightarrow7x-11=7\\ \Leftrightarrow x=\dfrac{18}{7}\)

( 7x - 11 ) ³ = ( -3 )² .15 + 208

( 7x - 11 ) ³ = 9 .15 + 208

( 7x - 11 ) ³ = 135 + 208

( 7x - 11 ) ³ = 343

( 7x - 11 ) ³ = 7³

=> 7x - 11 = 7

=> 7x = 7 + 11 = 18

=> x = 18/7

\(\left(7x-11\right)^3=\left(-3\right)^2.15+208\)

\(\Leftrightarrow\)\(\left(7x-11\right)^3=9.15+208\)

\(\Leftrightarrow\)\(\left(7x-11\right)^3=135+208\)

\(\Leftrightarrow\)\(\left(7x-11\right)^3=343\)

\(\Leftrightarrow\)\(\left(7x-11\right)^3=7^3\)

\(\Leftrightarrow\)\(7x-11=7\)

\(\Leftrightarrow\)\(7x=18\)

\(\Leftrightarrow\)\(x=\frac{18}{7}\)

Vậy \(x=\frac{18}{7}\)

Chúc bạn học tốt ~ 

trả lời:

B = 7x( 5/2x7 + 4/7x11 + 3/11x14 + 1/14x15 + 13/15x28 )

B = 7x(1/2 - 1/7 + 1/7 - 1/11 +....+ 1/15 - 1/28)

B = 7x(1/2 - 1/28)

B = 7x13/28

B = 13/4

Bàì làm:

\(B=\frac{5}{2.1}+\frac{4}{1.11}+\frac{3}{11.2}+\frac{1}{2.15}+\frac{13}{15.4}\)

\(B=7.\left(\frac{5}{2.7}+\frac{4}{7.11}+\frac{3}{11.14}+\frac{1}{14.15}+\frac{13}{15.28}\right)\)

\(B=7.\left(\frac{1}{2}-\frac{1}{7}+\frac{1}{7}-\frac{1}{11}+\frac{1}{11}-\frac{1}{14}+\frac{1}{14}-\frac{1}{15}+\frac{1}{15}-\frac{1}{28}\right)\)

\(B=7.\left(\frac{1}{2}-\frac{1}{28}\right)\)

\(B=7.\frac{13}{28}\)

\(B=\frac{13}{4}\)

Bài làm:

\(B=\frac{5}{2.1}+\frac{4}{1.11}+\frac{3}{11.2}+\frac{1}{2.15}+\frac{13}{15.4}\)

\(B=7\left(\frac{5}{2.7}+\frac{4}{7.11}+\frac{3}{11.14}+\frac{1}{14.15}+\frac{13}{15.28}\right)\)

\(B=7\left(\frac{1}{2}-\frac{1}{7}+\frac{1}{7}-\frac{1}{11}+\frac{1}{11}-\frac{1}{14}+\frac{1}{14}-\frac{1}{15}+\frac{1}{15}-\frac{1}{28}\right)\)

\(B=7\left(\frac{1}{2}-\frac{1}{28}\right)=7.\frac{13}{28}=\frac{13}{4}\)

bài này dễ mà

bai nay hay nhung de

1) \(x=\frac{8}{-3}-\frac{1}{2}=\frac{-19}{6}\)

2) \(\left(\frac{-5}{3}\right)^3=\frac{-125}{27}\)

     \(\frac{-24}{35}.\frac{-5}{6}=\frac{4}{7}\)

Mà \(\frac{-125}{27}<0<\frac{4}{7}\)

=> \(x=0\)

3) \(\left(7.x-11\right)^3=343\)

=> \(\left(7.x-11\right)^3=7^3\)

=> \(7.x-11=7\)

=> \(x=\frac{7+11}{7}=\frac{18}{7}\)