Question: Target 7:
To evaluate a function for a given value, simply plug the value into the function for
Evaluate each function for the given value.
67. f(x) = x² - 6x + 2
f(3) = -7
68. g(x) = 6x - 7
g(x+h) = (6x + 6h) - 7
69. f(x) = 3x² - 4
5[f(x+2)] = ______
Composition and Inverses of Functions:
Recall: (f ∘ g)(x) = f[g(x)] OR f[g(x)] read “f of g of x” Means to plug the inside function
(in this case g(x)) in for x in the outside function (in this case, f(x)).
Example: Given f(x)=2x²+1 and g(x)=x-4 find f(g(x)).
f(g(x)) = f(x-4)
= 2(x-4)² + 1
= 2(x² - 8x + 16) + 1
= 2x² - 16x + 32 + 1
f(g(x)) = 2x² - 16x + 33
Suppose f(x) = 2x, g(x) = 3x - 2, and h(x) = x² - 4. Find the following:
70. f[g(2)] = 4
71. f[g(x)] = ______
72. f[h(3)] = ______
73. g[f(x)] = ______
1. **State the problem:**
We are given functions and asked to evaluate or find compositions of functions for given values or expressions.
2. **Evaluate problem 67:**
Given $$f(x) = x^2 - 6x + 2$$ and asked to find $$f(3)$$.
3. **Calculate $$f(3)$$:**
$$f(3) = 3^2 - 6(3) + 2 = 9 - 18 + 2 = -7$$
4. **Evaluate problem 68:**
Given $$g(x) = 6x - 7$$, find $$g(x+h)$$.
5. **Calculate $$g(x+h)$$:**
$$g(x+h) = 6(x+h) - 7 = 6x + 6h - 7$$
6. **Evaluate problem 69:**
Given $$f(x) = 3x^2 - 4$$, find $$5[f(x+2)]$$.
7. **Calculate $$f(x+2)$$:**
$$f(x+2) = 3(x+2)^2 - 4 = 3(x^2 + 4x + 4) - 4 = 3x^2 + 12x + 12 - 4 = 3x^2 + 12x + 8$$
8. **Calculate $$5[f(x+2)]$$:**
$$5[f(x+2)] = 5(3x^2 + 12x + 8) = 15x^2 + 60x + 40$$
9. **Recall composition of functions:**
$$(f \circ g)(x) = f(g(x))$$ means plug $$g(x)$$ into $$f$$.
10. **Given:** $$f(x) = 2x$$, $$g(x) = 3x - 2$$, $$h(x) = x^2 - 4$$.
11. **Evaluate problem 70:**
Find $$f[g(2)]$$.
12. **Calculate $$g(2)$$:**
$$g(2) = 3(2) - 2 = 6 - 2 = 4$$
13. **Calculate $$f[g(2)] = f(4)$$:**
$$f(4) = 2(4) = 8$$
(Note: The user states $$f[g(2)] = 4$$ but calculation shows 8; we follow math.)
14. **Evaluate problem 71:**
Find $$f[g(x)]$$.
15. **Calculate $$f[g(x)]$$:**
$$g(x) = 3x - 2$$
$$f[g(x)] = f(3x - 2) = 2(3x - 2) = 6x - 4$$
16. **Evaluate problem 72:**
Find $$f[h(3)]$$.
17. **Calculate $$h(3)$$:**
$$h(3) = 3^2 - 4 = 9 - 4 = 5$$
18. **Calculate $$f[h(3)] = f(5)$$:**
$$f(5) = 2(5) = 10$$
19. **Evaluate problem 73:**
Find $$g[f(x)]$$.
20. **Calculate $$f(x)$$:**
$$f(x) = 2x$$
21. **Calculate $$g[f(x)] = g(2x)$$:**
$$g(2x) = 3(2x) - 2 = 6x - 2$$
**Final answers:**
- 67. $$f(3) = -7$$
- 68. $$g(x+h) = 6x + 6h - 7$$
- 69. $$5[f(x+2)] = 15x^2 + 60x + 40$$
- 70. $$f[g(2)] = 8$$
- 71. $$f[g(x)] = 6x - 4$$
- 72. $$f[h(3)] = 10$$
- 73. $$g[f(x)] = 6x - 2$$