To find a single equation for a given curve using MATLAB, a piecewise linear function can be utilized, such as f(x) = x/2000 for x ≤ 4000 and f(x) = 2 for x > 4000. For a more unified expression, the Heaviside function H(x) can be applied, allowing for the formulation f(x) = x/20000 + H(x - 4000)(4000 - x/2000). This approach effectively differentiates the behavior of the function based on the value of x. The discussion highlights the versatility of MATLAB in modeling curves through mathematical expressions.