Composition of Functions: f(x) = 3x, g(x) = 6x + 2x

[Kogsug]

can anyone help me with figuring what to do. i just started this stuff today in class.
find f(x) and g(f(x)) for x=3

f(x)=3x
g(x)=6x+2x

thank you

 

[stapel]

find f(x) and g(f(x)) for x=3

For f(3), plug "3" in for "x" in the formula for f(x), and simplify.

For g(f(3)), take the value you got for "f(3)", plug this in for "x" in the formula for g(x), and simplify.

Eliz.

 

[Kogsug]

ok so f(3)=3(3)=9 but what do i do with the "f(3)"?

 

[pka]

Find g(9)!

 

[jonboy]

Stapel gave you an exuberant explanation. As Stapel said "take the value you got for "f(3)", plug this in for "x" in the formula for g(x), and simplify".

So:

g(9)=6(9)+2(9)

 

[Kogsug]

g(f(3))=g(9)+2(9)^2

so 54+2(87)= 54+162=216 is this right?

 

[pka]

Yes, that is almost correct.
[I suspected that you had failed to include the <SUP>2</SUP>]
9<SUP>2</SUP>=81.

 

[Kogsug]

thank you

 

[stapel]

Stapel gave you an exuberant explanation.

I gave a "joyously unrestrained and enthusiastic" explanation...? :shock:

Eliz.

 

[jonboy]

No you gave a Lavish; extravagant (#2) explanation.

 

[stapel]

No you gave a Lavish; extravagant (#2) explanation.

If that was "lavish", I'd hate to see "sparse". :roll:

Eliz.