The second derivative, well, this was the same function as this right over here. So let me rewrite it. So a prime, the derivative of our combined area, was equal to the square root of 3 over 18x plus 1 8th x minus 12.5. The second derivative is going to be square root of 3 over 18 plus 1 over 8. So this thing right over here is greater than 0, which means we're concave upward for all x's. Which means for all x's, we're kind of doing a situation like this. So if we find an x where the slope is 0, it's going to be over an interval where it's concave upwards.