Question

how to tell if a graph is an exponential function

Answer 1

Look for e^x
also graph will be always increasing or decreasing
this is sure that log of values at ponits in will be in arithimetic progression

Answer 2

Its goes so high value in few steps .. for example e^10 = 22026.46
while e^2 = 7.2

by the way .. the high value is represent -ve values and +ve values
I hope its clear .