Question

I have this weird question that has to do with linear equations (I think), and this is what it says.

Let f(x) = 4x - 5

A. Find f(3)
B. Find x when f(x) = -21

Can somebody help me understand this??

Answer 1

f(x) tells you what f is for any value of x. So, f(3) means you substitute 3 wherever you see x:

f(x) = 4x-5
f(3) = 4(3)-5 = 12-5 = 7
f(0) = f(0)-5 = -5
etc.

So, if f(x) = -21, you have
-21 = 4x-5
-16 = 4x
x = -4