Đáp án + Giải thích các bước giải:
Bài `50`:
b, `(12/25)^x = (5/3)^(-2) - (-3/5)^4`
`(12/25)^x = (3/5)^2 - (3/5)^4`
` (12/25)^x = 9/25 - 81/625`
` (12/25)^x = 225/625 - 81/625`
` (12/25)^x = 144/625`
` (12/25)^x = (12/25)^2`
`=> x = 2`
Vậy `x = 2`
c, `(-3/4)^(3x - 1) = 256/81`
`(-3/4)^(3x - 1) = (4/3)^4`
`=> (-3/4)^(3x - 1) = (-3/4)^(-4)`
`=> 3x - 1 = -4`
`=> 3x = -3`
`=> x = -1`
Vậy `x = -1`
d, `172x^2 - 7^9 : 98^3 = 2^(-3)`
` 172x^2 - 7^9 : 7^6 : 2^3 = 1/8`
` 172x^2 - 7^3 : 2^3 = 1/8`
` 172x^2 - (7/2)^3 = 1/8`
` 172x^2 = 1/8 + (7/2)^3`
` 172x^2 = 1/8 + 343/8`
` 172x^2 = 344/8`
` 172x^2 = 43`
` x^2 = 43 : 172`
` x^2 = 1/4`
`=> x = \pm 1/2`
Vậy `x \in {1/2 ; -1/2}`
