Đáp án: Bài 2 : a ) n = 3 , 4 ; b ) n = 5
Bài 3 : $\frac{-1}{3}$
Giải thích các bước giải:
Bài 2 :
a ) 2 . 16 > $2^{n}$ > 4
32 > $2^{n}$ > 4
$2^{5}$ > $2^{n}$ > $2^{2}$
→ 5 > n > 2
→ n = 3 , 4
b ) 9 . 27 ≤ $3^{n}$ < 81 . $3^{2}$
$3^{2}$ . $3^{3}$ ≤ $3^{n}$ < $3^{4}$ . $3^{2}$
$3^{5}$ ≤ $3^{n}$ < $3^{6}$
→ 5 ≤ n < 6
→ n = 5
Bài 3 :
A = $\frac{4^5.9^4-2.6^9}{2^{10} .3^8+6^8.20}$
A = $\frac{2^{10}.3^8-2.3^9.2^9}{2^{10}.3^8+2^8.3^8.20}$
A = $\frac{2^{10}.3^8-2^{10}.3^9}{2^{10}.3^8+2^8.3^8.20}$
A = $\frac{2^8.3^8(2^2-2^2.3)}{2^8.3^8(2^2+20)}$
A = $\frac{2^2-2^2.3}{2^2+20}$
A = $\frac{4-4.3}{4+20}$
A = $\frac{4-12}{24}$
A = $\frac{-8}{24}$
A = $\frac{-1}{3}$
