2(x)^x = ??

4^x - 4^(x-1) = 24
4^x -4^x/4 =24
4*4^x-4^x=96
3*4^x=96
4^x=32
(2^2)^x=2^5
2^2x=2^5

Thus, 2x=5
x=2.5

2(2.5)^2.5
=19.8(corr to 3 sig. fig.)

我搵到個x=2.5
但係我計到個答案唔係整數
答案係=19.76423538