Bài $1$.
$a$) `(2^2 : 4 ) . 2x = 4`
`⇔ (4 : 4) . 2x = 4`
`⇔ 2x = 4`
`⇔ x = 2`
Vậy `x=2`
$b$) `1/2 .2^x +4 . 2^x = 9 . 2^5`
`⇔ 2^x . 9/2 = 288`
`⇔ 2^x = 64`
`⇔ x = 6`
Vậy `x=6`
Bài $2$.
$a$) `A = (7^{1997} - 7^{1995}) : (7^{1997} . 7)`
`A = [7^{1995} . (7^2 - 1)] : 7^{1998}`
`A = \frac{48}{7^{3}}`
`A = {48}/{343}`
$b$) `(2^8+8^2):(2^5-2^3)`
`= 320:24`
`= 40/3`