Answer :
We need to remember that the general equation for the exponential model is given by:
y= a b^x
Where a is different from 0
b >0
b different from 1
Based on this the correct answers for this case are:
y = -5 (7)^x (Yes)
y = -5 (-7)^x (No)
y= 2(pi)^x+1 = 2pi (pi)^x (Yes)
y= -5 (x)^7 (No)