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222-9+11+12:2*14+14 = ? ( )

Toán Lớp 12: giải pt a) 3.$9^{x}$ -2.$15^{x}$ -5.$25^{x}$ =0 b) 3.$16^{x}$ +2.$81^{x}$ =5.$36^{x}$

Tháng Năm 3, 2022 Toán học 1 Comment 0 views

Toán Lớp 12: giải pt
a) 3.$9^{x}$ -2.$15^{x}$ -5.$25^{x}$ =0
b) 3.$16^{x}$ +2.$81^{x}$ =5.$36^{x}$

Comments ( 1 )

  1. diemmyhoa
    diemmyhoa
    3 Tháng Năm, 2022 at 2:27 sáng
    Reply
    $a)\quad 3.9^x – 2.15^x – 5.25^x = 0$
    $\Leftrightarrow 3.\left(\dfrac35\right)^{2x} – 2.\left(\dfrac35\right)^x – 5 = 0$
    $\Leftrightarrow \left[\begin{array}{l}\left(\dfrac35\right)^x= -1\quad (vn)\\\left(\dfrac35\right)^x=\dfrac53\end{array}\right.$
    $\Leftrightarrow x = -1$
    Vậy $S =\{-1\}$
    $b)\quad 3.16^x + 2.81^x = 5.36^x$
    $\Leftrightarrow 3.\left(\dfrac23\right)^{4x} – 5.\left(\dfrac23\right)^{2x} + 2 = 0$
    $\Leftrightarrow \left[\begin{array}{l}\left(\dfrac23\right)^{2x}= 1\\\left(\dfrac23\right)^{2x}=\dfrac23\end{array}\right.$
    $\Leftrightarrow \left[\begin{array}{l}2x = 0\\2x = 1\end{array}\right.$
    $\Leftrightarrow \left[\begin{array}{l}x = 0\\x =\dfrac12\end{array}\right.$
    Vậy $S =\left\{0;\dfrac12\right\}$

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222-9+11+12:2*14+14 = ? ( )

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