Hello Asma
Take a look at the following
>> 1:8 ans = 1 2 3 4 5 6 7 8
>> -1:-8 ans = 1×0 empty double row vector
>> -1:-1:-8 ans = -1 -2 -3 -4 -5 -6 -7 -8
Matlab assumes by default that indices are incremented by +1. If you want to decrement by -1 you have to supply that information as on the last line. That change gets the for loop going. However, you are not saving the answer for different values of k. Values can be saved in an array z, but indices that address an array must be positive. So it's better to have positive values of k and adjust accordingly.
z = zeros(1,8) % make an initial z array
for k = 1:8
h = 10.^(-k)
z(k) = (exp(1+h) - exp(1))./h
end
disp(z)
There is no need to define a new function for exp since you can just use exp directly.
