Composite function

I'm having trouble with these 2 composite function questions

Find the requested composite function value

1.f(x) = 7x + 8, g(x) = -2/x; find (g * f)(3)

2.f(x) = x-6/10, g(x) = 10x + 6; find(g * f)(X)

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Originally Posted by jay05

I'm having trouble with these 2 composite function questions

Find the requested composite function value

1.f(x) = 7x + 8, g(x) = -2/x; find (g * f)(3)

2.f(x) = x-6/10, g(x) = 10x + 6; find(g * f)(X)

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You say "composite functions" but use a standard multiplication symbol (*). Hopefully you mean composition, because that's what follows!
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1. g(f(3)) can be found by first determining f(3), then finding "g of" this value.
f(3) = 7(3) + 8 = 21 + 8 = 29. g(f(3)) = g(29) = -2/29.

2. g(f(x)) = g((x - 6)/10) = ... can you take it from here?

Quote:

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Originally Posted by jay05

I'm having trouble with these 2 composite function questions

Find the requested composite function value

1.f(x) = 7x + 8, g(x) = -2/x; find (g * f)(3)

2.f(x) = x-6/10, g(x) = 10x + 6; find(g * f)(X)

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What have you tried? Where are you stuck? Do you uderstand the notation (is it explained in your class notes or textbook?) Does * mean you're multiplying the two functions together ....?

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Originally Posted by TheChaz

You say "composite functions" but use a standard multiplication symbol (*). Hopefully you mean composition, because that's what follows!
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1. g(f(3)) can be found by first determining f(3), then finding "g of" this value.
f(3) = 7(3) + 8 = 21 + 8 = 29. g(f(3)) = g(29) = -2/29.

2. g(f(x)) = g((x - 6)/10) = ... can you take it from here?

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the second x is kind of throwing me off, is x still equivalent to 1?
if so those the equation = 1?

Which question are we talking about?
x is not equivalent (or equal) to 1 in either question. Where did you come up with that?

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Originally Posted by jay05

the second x is kind of throwing me off, is x still equivalent to 1?
if so those the equation = 1?

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Please address the questions I asked in post #3 if you need more help.

the second question and i just thought that x = 1 like it did in previous algebra problems

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Originally Posted by mr fantastic

What have you tried? Where are you stuck? Do you uderstand the notation (is it explained in your class notes or textbook?) Does * mean you're multiplying the two functions together ....?

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i understand the notation just having trouble with this and no * doesnt mean multiplication i just didnt know what to put in the middle

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Originally Posted by jay05

the second question and i just thought that x = 1 like it did in previous algebra problems

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This is bothering me. In which algebra problems did x = 1?

In question (2), no x-values are specified, so we will end up with g(f(x)) = [some function of x].
You can certainly determine the value of this function WHEN x = 1, but to say that x is equal to 1 is not correct.

Quote:

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Originally Posted by jay05

I'm having trouble with these 2 composite function questions

Find the requested composite function value

1.f(x) = 7x + 8, g(x) = -2/x; find (g * f)(3)

2.f(x) = x-6/10, g(x) = 10x + 6; find(g * f)(X)

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. Substsitute x = 3 and get the value.

Alternatively, f(3) = 29. Therefore g(f(3)) = g(29) = -2/29.

Do the other one in the same way.