So i used the first derivative test and received (x+5)1/2-sqrtx/(sqrtx(x+5)) and set (x+5)-sqrtx to zero then i combined like terms and received sqrtx + 5 = 0 then sqrtx^2 = 5^ and x = 25

However, this is not where the derivative is decreasing. My question is where I went wrong, it seems like everything I did was perfectly legal to come up with 25 but it turned out wrong. Any help would be appreciated