I didn't work fractions out 
Restarting the project...
now i have a better understanding of one-variable calculus :)(specifyed that cuz still doesnt know what the multi variable one is)
I had to re-read the entire thread to figure out that you meant differential calculus and not lambda calculus! :~/
Suppose you have some function of two variables f(x,y). For example, you put some magnets in a plane and then for any point on the plane you can figure out the magnetic field (a vector). You want to find a point at which the field magnitude |f(x,y)| is smallest. What do you do? You know how to hold y constant and then find the minimum x for that value of y. Then you could take the function g(y₀) = x such that f(x,y₀) is minimum, and compute the minimum of that, another single-variable function. So you have a candidate for the minimum point: (g(y₀), y₀). But what if instead you start by holding x constant, finding the y for which |f(x₀, y)| is minimal, etc. Now you have two ways to compute the minimum. Are they guaranteed to give the same answer? Or is there some other computation that varies x and y at the same time? This is multivariable differential calculus. (Unsurprisingly, there's also multivariable integral calculus to go with it.)
Whoops!Got stuffed with thousands of messages and this one accidentally flown away!
Also now i also figured out mvc by myself cuz wanting to integral a complex number which stores a position