And so I can just rewrite this expression as x is less than or equal to c as a function of delta x, which is less than or equal to x plus delta x. So now you see that c is always sandwiched between x and x plus delta x. Well what's the limit of x as delta x approaches 0? Well x isn't dependent on delta x in any way. So this is just going to be equal to x. What's the limit of x plus delta x as delta x approaches 0? Well as delta x approaches 0, this is just going to be equal to x.