Math  /  Algebra

QuestionFind (fg)(x)(f \circ g)(x) and (gf)(x)(g \circ f)(x). f(x)=3x21,g(x)=2xf(x)=-3 x^{2}-1, g(x)=2 x (fg)(x)=(f \circ g)(x)= \square (Simplify your answer.)

Studdy Solution

STEP 1

1. We are given two functions f(x)=3x21 f(x) = -3x^2 - 1 and g(x)=2x g(x) = 2x .
2. We need to find the composition of these functions in two different orders: (fg)(x) (f \circ g)(x) and (gf)(x) (g \circ f)(x) .
3. The composition of functions involves substituting one function into another.

STEP 2

1. Calculate (fg)(x) (f \circ g)(x) .
2. Calculate (gf)(x) (g \circ f)(x) .

STEP 3

To find (fg)(x) (f \circ g)(x) , substitute g(x) g(x) into f(x) f(x) .
(fg)(x)=f(g(x))=f(2x) (f \circ g)(x) = f(g(x)) = f(2x)

STEP 4

Substitute 2x 2x into the function f(x)=3x21 f(x) = -3x^2 - 1 .
f(2x)=3(2x)21 f(2x) = -3(2x)^2 - 1

STEP 5

Simplify the expression:
(2x)2=4x2 (2x)^2 = 4x^2
f(2x)=3(4x2)1=12x21 f(2x) = -3(4x^2) - 1 = -12x^2 - 1
Therefore, (fg)(x)=12x21 (f \circ g)(x) = -12x^2 - 1 .

STEP 6

To find (gf)(x) (g \circ f)(x) , substitute f(x) f(x) into g(x) g(x) .
(gf)(x)=g(f(x))=g(3x21) (g \circ f)(x) = g(f(x)) = g(-3x^2 - 1)

STEP 7

Substitute 3x21 -3x^2 - 1 into the function g(x)=2x g(x) = 2x .
g(3x21)=2(3x21) g(-3x^2 - 1) = 2(-3x^2 - 1)

STEP 8

Simplify the expression:
g(3x21)=2(3x2)+2(1)=6x22 g(-3x^2 - 1) = 2(-3x^2) + 2(-1) = -6x^2 - 2
Therefore, (gf)(x)=6x22 (g \circ f)(x) = -6x^2 - 2 .
The solutions are: (fg)(x)=12x21 (f \circ g)(x) = -12x^2 - 1 (gf)(x)=6x22 (g \circ f)(x) = -6x^2 - 2

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