Bài tập 2: Tìm x, biết:
a) $2^{x}.x=128$
b) $2x - 2^{6}=6$
c) $7^{2}.7^{x}=7^{4}$
d) $3^{x}+25 = 26.2^{2}+2.3^{0}$
Bài Làm:
a) $2^{x}.4=128$
$\Rightarrow 2^{x} =128:4$
$\Rightarrow 2^{x} = 32$
$\Rightarrow 2^{x}=2^{5}$
$\Rightarrow x =5$
b) $2x - 2^{6}=6$
$\Rightarrow 2x - 64 = 6$
$\Rightarrow 2x = 6 + 64$
$\Rightarrow 2x = 70$
$\Rightarrow x = 70:2$
$\Rightarrow x = 35$
c) $7^{2}.7^{x}=7^{4}$
$\Rightarrow 7^{x} = 7^{4}:7^{2}$
$\Rightarrow 7^{x} = 7^{2}$
$\Rightarrow x = 2$
d) $3^{x}+25 = 26.2^{2}+2.3^{0}$
$\Rightarrow 3^{x}+25 = 26.4 + 2.1$
$\Rightarrow 3^{x} +25 = 104 + 2$
$\Rightarrow 3^{x}+25 = 106$
$\Rightarrow 3^{x} = 106 -25$
$\Rightarrow 3^{x} = 81$
$\Rightarrow 3^{x} = 3^{4}$
$\Rightarrow x = 4$