So this is going to be the square root of 3 times x squared over, let's see, this is 4 times 9. This is x squared over 9. So this is going to be 4 times 9 is 36. And then over here in blue, this is going to be plus 100 minus x squared over 16. Now let's take the derivative of this. So a prime, our combined area, the derivative of our combined area as a function of x, is going to be equal to, well, the derivative of this with respect to x is just going to be square root of 3x over 18. The derivative of this with respect to x was the derivative of something squared over 16 with respect to that something.