I need to substitute two different points (-1,8) and (-8, 1) from a graph into the exponential function y=Ae^kx

I swear we never even learned this in class, and the internet is really confusing me, so help is much appreciated!

Question

I need to substitute two different points (-1,8) and (-8, 1) from a graph into the exponential function y=Ae^kx

I swear we never even learned this in class, and the internet is really confusing me, so help is much appreciated!

anonymous · Answer

not sure what you mean
you have to determine the function?

kayla0297 · Answer

Yes, I have the graph but I must determine the function from those two points. Sorry for the confusion!

anonymous · Answer

ok we can do it

anonymous · Answer

we have 
$$8=Ae^{-k}\
1=Ae^{-8k}$$

anonymous · Answer

so far so good?

anonymous · Answer

divide and get 
$$8=\frac{Ae^{-k}}{Ae^{-8k}}$$ or 
$$8=e^{7k}$$

anonymous · Answer

solve for$k$  
if you are confused by any step let me know

kayla0297 · Answer

Okay, so the answer I get for k is 0.3, but how do I now solve for A?

bradely · Answer

y=Ae^kx 8=Ae^(0.3)(-1) 8=Ae^(-0.3) A =8/e^(-0.3) Source: http://www.mathskey.com/question2answer/

kayla0297 · Answer

Which equals 10.8. I can verify this with my graphics calculator, but drawing y=10.8e^0.3x does not show the right equation of the line I am supposed to be finding. perhaps I did something wrong finding the constant (k)?

kayla0297 · Answer

(to the person who deleted their comments) That gives me exactly the same answer, doesn't it? I do not get what I am doing wrong...

kayla0297 · Answer

Since no one else wants to help me, I am closing this.