# Problem finding intersection with exponential function

Hampus Hedenberg shared this question 2 years ago

Hi,

I am having trouble using the Intersect tool. I have drawn two graphs:

y=400e^(0.07x)

y=2000

There is (of course) an intersection, but GeoGebra only gives me "undefined". If I change the second graph to y=1000 the program gives me the intersection (13.09, 1000) as expected. (1) Why cannot GeoGebra find the first intersection?

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I then started over and wrote it as two functions:

f(x)=400e^(0.07x)

g(x)=2000

The intersection (22.99, 2000) could now be found without any problem. (2) Why is GeoGebra able to solve this but not the first?

Thank you for the help. Screenshots of my trials are attached.

1

curves and lines are another type of objects than functions on which you can apply calculations as derivate etc. This gives the opportunity to apply or exclude some numeric calculation methods on both types. And the limits of these numeric methods start to show up when the numbers get bigger.

So it's good to know (or to experience) when to use functions or not.

chris

1

So the conclusion to this is that GeoGebra does not find intersect with y=a in the same way as with h(x)=a, so to always find the intersect between an (exponential) function and a line, the line must also be input as a function, like h(x)=a?

What about intersect between (exponential) function and the line x=a?

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