The derivative of sec x is sec x tan x. This means that if we want to find the derivative of sec x with respect to x, we can write it as d/dx(sec x) = sec x tan x. It is important to note that sec x is the reciprocal of cos x, and tan x is the ratio of sin x to cos x. Another way to derive the derivative of sec x is to use the quotient rule and the chain rule. The quotient rule states that the derivative of f(x)/g(x) is (g(x)f(x) - f(x)g(x))/. By applying these rules, we can show that the derivative of sec x is sin x/cos^2 x.