Given f(x) = 5x − 8, find the following:

Question

a:
f(−1)
b:
f(0)
c:
f(1)
d:
f(y)
e:
f(a + b)

Answer 1

The first four are easy. The last takes extra work, but they all follow the same method. Notice the original function:

f(X) = 5X - 8

What changed when they wrote:

A) f(-1) ? 

The X vanished, replaced with -1. They did it on the left, so you must do the same on the right:

    f(-1) = 5(-1) - 8 = -5 -8 = -13

Use the same approach for B, C, and yes -- even D! You will get a weird answer, but you are still just replacing "X" with "Y". 

E) This looks especially strange, but don't let it frighten you! We replaced "X" with "a+b":
   f(a+b) = 5(a+b) - 8 = 5a + 5b - 8

All done!