Question

given f(x)=3x-5 and g(x)=2x^2+5x and h(x)=1/(x+3) find:

ff(-2)
=(3(-2)-5)(3(-2)-5)
=(-6-5)(-6-5)
=121

is this correct or is it wrong? I don't really know how to write ff(-2)

x if f(x)=-7
=???

I don't know how to start this


please help and thank you

Answer 1

ff(-2) is usually written f(f(-2)) or (fof)(-2). Don't you have any textbook which shows this?

So, just plug in symbols one level at a time.

f(x) = 3x-5, so
f(f(x)) = 3f(x)-5 = 3(3x-5)-5 = 9x-15-5 = 9x-20
so, (fof)(-2) = 9(-2)-20 = -18-29 = -38

or, you can do it the other way, and f(-2) = -11, so f(-11) = 3(-11)-5 = -33-5 = -38


now, if f(x) = -7,
7 = 3x-5
12 = 3x
x = 4