bài 1: Tìm số tự nhiên n biết a) 3 . 4^n : 2^3 = 384 b) 5^n . (1/5)^3 = 125 c) 4 . 3^n = 324 bài 2 tính a) (1/2)^3 . 4 + 3/4 b) 4^3 : 2^5 + 3^5 : 9^2 c) 7 - (-4/5) ^0 + (1/3) ^2 ; 2 d) (1/2) ^5 - (1,5)^2 + 31/32 + 102,25 e) 2^3 . (1/2) ^7 . 32 .28

`1)`

`a)3.4^n : 2^3 = 384`

`(2^2)^n : 2^3=384:3`

`2^{2n}:2^3=128`

`2^{2n-3}=2^7`

`->2n-3=7`

`->2n=7+3`

`->2n=10`

`->n=10:2`

`->n=5`

`-` Vậy : `n=5.`

`b)5^n . (1/5)^3=125`

`5^n =125 : 1/{5^3}`

`5^n = 5^3 . 5^3`

`5^n=5^6`

`->n=6`

`-` Vậy : `n=6.`

`c)4.3^n=324`

`3^n=324:4`

`3^n=81`

`3^n=3^4`

`->n=4`

`-` Vậy : `n=4.`

`············`

`2)`

`a)(1/2)^3 . 4+3/4`

`=1/{2^3} . 2^2+3/4`

`={2^2}/{2^3}+3/4`

`=1/2+3/4`

`=2/4+3/4`

`=5/4`

`b)4^3:2^5+3^5:9^2`

`=(2^2)^3:2^5+3^5:(3^2)^2`

`=2^6:2^5+3^5:3^4`

`=2+3`

`=5`

`c)7-(-4/5)^0+(1/3)^2:2`

`=7-1+1/9:2`

`=6+1/18`

`=108/18+1/18`

`=109/18`

`d)(1/2)^5 - (1,5)^2+31/32+102,25`

`=1/32-2,25+31/32+102,25`

`=(1/32+31/32)+(102,25-2,25)`

`=32/32+100`

`=1+100`

`=101`

`e)2^3 . (1/2)^7 . 32 . 28`

`=2^3 . 1/{2^7} . 2^5 . 2^2 . 7`

`=2^10 . 1/{2^7} . 7`

`={2^10}/{2^7} .7`

`=2^3 . 7`

`=8.7`

`=56`

`#Sal_tSea`