Marginal utility is just the extra happiness from one more taco. If your utility function is $U(T, R) = T^{0.5} \times R^{0.5}$, take the derivative with respect to T. That gives you: $MU_T = 0.5 \times T^{-0.5} \times R^{0.5}$. Don’t panic—it’s just math that looks like alien code. Do the same for ramen: $MU_R = 0.5 \times T^{0.5} \times R^{-0.5}$.
Here’s the fun part: these derivatives say, “Hey, if you have a lot of tacos already, one more taco isn’t that thrilling.” That’s the law of diminishing marginal utility—your first taco is heaven, your tenth is a comfort eating regret.
