c)
`(2x+1)^3. 2^2=500`
`(2x+1)^3. 4 =500`
`(2x+1)^3 =500:4`
`(2x+1)^3 =125`
`(2x+1)^3 =5^3`
` 2x+1 =5`
` 2x =5-1`
` 2x =4`
` x =4:2`
` x =2`
Vậy `x=2`
d) So sánh `5^30` và `3^50`
Ta có: `5^30 = (5^3)^10 = 125^10`
`3^50 = (3^5)^10 = 243^10`
Vì `125<243` nên `125^10<243^10` hoặc `5^30<3^50`
#Huy