The first thing we have to see is that exercise (c) is given as follows
From (e) we know:
So we replace f(k) of the (e) part on the (c) part as follows:
Now we must find the value of x the function F (k) is not defined. This value is given when the denominator of the function gives 0 since the function would be indeterminate then:
The domain of this function is indeterminate for k = 7/4 and this value is the one that must be excluded from the domain
All functions have a domain and a range. The domain of a function is all the values that the function can take along the k-axis and the range on the f(k)-axis.