Tìm x biết: a) $\frac{2}{3}x+3=\frac{1}{2}$ b) $3^{x+2}+2.3^{x}=297$
2 câu trả lời
`2/3x + 3 = 1/2`
`2/3x = 1/2 - 3`
`2/3x = -5/2`
`x = -5/2 : 2/3`
`x = -15/4`
Vậy `x = -15/4 `
`3^(x + 2 ) + 2 . 3^x = 297`
`3^x . 3^2 + 2 . 3^x = 297`
`3^x . ( 3^2 + 2 ) = 297`
`3^x . ( 9 + 2 ) = 297`
`3^x . 11 = 297`
`3^x = 297 : 11`
`3^x = 27`
`3^x = 3^3`
`x = 3`
Vậy `x = 3`
Đáp án:
$a)\,\dfrac23x+3=\dfrac12\\\Rightarrow \dfrac23x=\dfrac12-\dfrac62\\\Rightarrow\dfrac23x=\dfrac{-5}2\\\Rightarrow x=\dfrac{-5}2\!\cdot\!\dfrac32\\\Rightarrow x=\dfrac{-15}4$
Vậy $x=\dfrac{-15}4$.
$b)\,3^{x+2}+2.3^x=297\\\Rightarrow 3^x.3^2+2.3^x=297\\\Rightarrow 3^x.\!(9+2)=297\\\Rightarrow 3^x.11=297\\\Rightarrow 3^x=27\\\Rightarrow 3^x=3^3\\\Rightarrow x=3$
Vậy $x=3$.
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