High School

If [tex]f(x) = -12x^4 + 5x^2 - 45[/tex] and [tex]g(x) = 10x^4 - 70x^2 - 300[/tex], what is [tex](f-g)(x)[/tex]?

A. [tex]-2x^5 - 65x^3 - 345x[/tex]

B. [tex]-2x^4 - 65x^2 - 345[/tex]

C. [tex]-22x^5 + 75x^3 + 255x[/tex]

D. [tex]-22x^4 + 75x^2 + 255[/tex]

Answer :

We are given the functions

[tex]$$
f(x) = -12x^4 + 5x^2 - 45
$$[/tex]

and

[tex]$$
g(x) = 10x^4 - 70x^2 - 300.
$$[/tex]

To find [tex]$(f - g)(x)$[/tex], we subtract [tex]$g(x)$[/tex] from [tex]$f(x)$[/tex]:

[tex]$$
(f - g)(x) = f(x) - g(x).
$$[/tex]

Substitute the expressions for [tex]$f(x)$[/tex] and [tex]$g(x)$[/tex]:

[tex]$$
(f - g)(x) = \left(-12x^4 + 5x^2 - 45\right) - \left(10x^4 - 70x^2 - 300\right).
$$[/tex]

Next, remove the parentheses. Be careful with the negative sign before the second set of parentheses:

[tex]$$
(f - g)(x) = -12x^4 + 5x^2 - 45 - 10x^4 + 70x^2 + 300.
$$[/tex]

Now, combine like terms starting with the [tex]$x^4$[/tex] terms, then the [tex]$x^2$[/tex] terms, and finally the constant terms:

1. Combine the [tex]$x^4$[/tex] terms:
[tex]$$
-12x^4 - 10x^4 = -22x^4.
$$[/tex]

2. Combine the [tex]$x^2$[/tex] terms:
[tex]$$
5x^2 + 70x^2 = 75x^2.
$$[/tex]

3. Combine the constant terms:
[tex]$$
-45 + 300 = 255.
$$[/tex]

Thus, the simplified form is

[tex]$$
(f - g)(x) = -22x^4 + 75x^2 + 255.
$$[/tex]

So the correct answer is

[tex]$$
-22x^4 + 75x^2 + 255.
$$[/tex]