Diketahui dua fungsi yaitu f(x) = x^2 + 4x + 4 dan g(x) = 2x^2 - 8. Tentukan: a) (fog)(x) b) (gof)(x) c) (fof)(x) d) (gog)(x)
Solution
The problem involves two functions, f(x)=x2+4x+4 and g(x)=2x2−8, and it asks to determine the following composite functions:
(f∘g)(x)
(g∘f)(x)
(f∘f)(x)
(g∘g)(x)
Let's solve each part:
a) (f∘g)(x)=f(g(x))
This means substituting g(x) into f(x):
g(x)=2x2−8
Now, substitute g(x) into f(x):
f(g(x))=(2x2−8)2+4(2x2−8)+4
Expand each term:
(2x2−8)2=4x4−32x2+644(2x2−8)=8x2−32
Now, substitute back:
f(g(x))=(4x4−32x2+64)+(8x2−32)+4
Simplify:
f(g(x))=4x4−24x2+36
b) (g∘f)(x)=g(f(x))
This means substituting f(x) into g(x):
f(x)=x2+4x+4
Now, substitute f(x) into g(x):
g(f(x))=2(x2+4x+4)2−8
Expand (x2+4x+4)2:
(x2+4x+4)2=x4+8x3+24x2+32x+16
Now substitute:
g(f(x))=2(x4+8x3+24x2+32x+16)−8
Expand and simplify:
g(f(x))=2x4+16x3+48x2+64x+32−8g(f(x))=2x4+16x3+48x2+64x+24
c) (f∘f)(x)=f(f(x))
This means substituting f(x) into f(x):
f(f(x))=(x2+4x+4)2+4(x2+4x+4)+4
Expand (x2+4x+4)2 as before:
(x2+4x+4)2=x4+8x3+24x2+32x+16
Now, substitute back:
f(f(x))=(x4+8x3+24x2+32x+16)+4(x2+4x+4)+4
Expand:
4(x2+4x+4)=4x2+16x+16
Now, combine terms:
f(f(x))=x4+8x3+28x2+48x+36
d) (g∘g)(x)=g(g(x))
This means substituting g(x) into g(x):
g(g(x))=2(2x2−8)2−8
Expand (2x2−8)2:
(2x2−8)2=4x4−32x2+64
Now, substitute back:
g(g(x))=2(4x4−32x2+64)−8
Expand and simplify:
g(g(x))=8x4−64x2+128−8g(g(x))=8x4−64x2+120
Final answers:
(f∘g)(x)=4x4−24x2+36
(g∘f)(x)=2x4+16x3+48x2+64x+24
(f∘f)(x)=x4+8x3+28x2+48x+36
(g∘g)(x)=8x4−64x2+120
Would you like further details or have any questions?
Here are 5 related questions:
How do you compute the derivative of composite functions like (f∘g)(x)?
What is the difference between (f∘g)(x) and (g∘f)(x)?
How would you solve for roots in these composite functions?
Can you determine the inverse function for f(x) or g(x)?
What happens when you take the second derivative of (f∘g)(x)?
Tip: When dealing with composite functions, always substitute carefully and simplify the expression step by step to avoid errors.