tìm x biết 2^2 . 3^3x – 27^x = 9^5 b,2^x : 2 = 256 c,(x^2)^4 . 16 = 2^20

$a$) $2^2 . 3^{3x} – 27^x = 9^5$

$⇔ 4 . 3^{3x} – (3^3)^x = (3^2)^5$

$⇔ 4 . 3^{3x} – 3^{3x} = 3^{10}$

$⇔ 3^{3x} . (4 – 1) = 3^{10}$

$⇔ 3^{3x} . 3 = 3^{10}$

$⇔ 3^{3x+1} = 3^{10}$

$⇔ 3x+1=10$

$⇔ 3x = 9$

$⇔ x = 3$.

  Vậy $x=3$

$b$) $2^x : 2  = 256$

$⇔ 2^x : 2 = 2^8$

$⇔ 2^x = 2^8 . 2$

$⇔ 2^x = 2^9$

$⇔ x = 9$

  Vậy $x=9$.

$c$) $(x^2)^4 . 16 = 2^{20}$

$⇔ x^8 . 2^4 = 2^{20}$

$⇔ x^8 = 2^{20} : 2^4$

$⇔ x^8 = 2^{16}$

$⇔ x^8 = (2^2)^8$

$⇔ x = 2^2$

$⇔ x = 4$

  Vậy $x=4$.