`#3107`
`a)`
`(x - 20)^3 = -64`
`\Rightarrow (x - 20)^3 = (-4)^3`
`\Rightarrow x - 20 = -4`
`\Rightarrow x = -4 + 20`
`\Rightarrow x = 16`
Vậy, `x = 16.`
`b)`
`9(x + 1) - 11(x + 7) = 105 - 1`
`\Rightarrow 9(x + 1) - 11(x + 7) = 104`
`\Rightarrow 9x + 9 - 11x - 77 = 104`
`\Rightarrow (9 - 11)x + (9 - 77) = 104`
`\Rightarrow -2x - 68 = 104`
`\Rightarrow -2x = 104 + 68`
`\Rightarrow -2x = 172`
`\Rightarrow x = 172 \div (-2)`
`\Rightarrow x = -86`
Vậy,` x = -86.`
a) Ta có ( x - 20 )3 = -64 = ( -4 )3
⇒ x - 20 = -4
⇒ x = 20 + ( -4 ) = 16
b) Ta có 9 ( x + 1 ) - 11 ( x + 7 ) = 105 - 1
⇒ 9x + 9 - 11x - 77 = 104
⇒ ( -2 ) . x - 68 = 104
⇒ ( -2 ) . x = 104 - 68 = 36
⇒ x = 36 : ( -2 ) = -18
a)
\(\left(x-20\right)^3=-64\)
\(\left(x-20\right)^3=-4^3\)
\(\Rightarrow x-20=-4\)
\(\Rightarrow x=-4+20=16\)
b)
\(9\left(x+1\right)-11\left(x+7\right)=105-1\)
\(9\left(x+1\right)-11\left(x+1+6\right)=104\)
\(9\left(x+1\right)-11\left(x+1\right)+66=104\)
\(\left(x+1\right).\left(9-11\right)=104-66\)
\(\left(x+1\right).\left(-2\right)=38\)
\(x+1=38:\left(-2\right)\)
\(x+1=-19\)
\(x=-19-1\)
\(x=-20\)
