Or another way to think about it, if your derivative is increasing over an interval, then you're concave up on that interval. And so we here, we have a graph of the derivative, and it is indeed increasing over that interval. So our calculus-based justification that we'd wanna use is that, look, f, which is g prime, is increasing on that interval. The derivative is increasing on that interval, which means that the original function is concave up. F is positive on that interval. That's not sufficient, that's not a sufficient calculus-based justification, because if your derivative is positive, that just means your original function is increasing, it doesn't tell you that your original function is concave up. F is concave up on the interval.