looking for a decreasing mathematical function

Factual Questions
1

I just want to see some general plots of mathematical functions, so I can compare them side by side.

I don’t need a websight that will plot a specific function nor do I need a graphing calculator. I just want to look at pictures and say “oooh, I like how that one tends to drop off”

Specifically the reason is I want to include a particular function as a model showing how desirable a car is related to its odometer reading. The relationship isn’t linear; 5000miles is a lot more desirable than 20000; and anything greater than 50,000 is essentially not desirable at all. I don’t know if I want to use a square root function, inverse log, exponential, fraction or combination of a few things.

While I will welcome suggestions for the type of mathematical relationship I’m looking for, I’m mostly wanting an easy way to compare a bunch of plots so I can decide for myself (that’s most of the fun)

any slick websites out there that just give me examples of functions and their plots?

2

m/(x+m)
x is number of miles and m is a constant that you choose. m is the mileage that things really start to be undesirable.

If you want it to roll off faster try something like
m^2/(x+m)^2 or m^3/(x+m)^3

3

Or you could do something in the general form of:

y = C - x^2

to get an upside down parabola shape.

(you can change x^2 to another exponent for different rates of change.)

4

How about y=c-2^x ?

5

I think you want something like the logistic function: mileage doesn’t matter so much if you have too much or too little, but there’s a range in the middle where it makes all the difference in the world.