Answer:
2. Eunju is right
3. [tex]x^2+5x+6[/tex] is a factor of [tex]x^4+5x^3+2x^2-20x-24[/tex].
Step-by-step explanation:
Polynomial Remainder Theorem
The polynomial remainder theorem states that the remainder of the division of a polynomial f(x) by (x-a) is equal to f(a).
As a consequence, if a polynomial is divisible by x-a, f(a)=0.
Part 1:
Let's make:
[tex]f(x)=(x+b)^3+(x+c)^2-(b-c)[/tex]
To find out if x+b is a factor of f(x), we find f(-b):
[tex]f(-b)=(-b+b)^3+(-b+c)^2-(b-c)[/tex]
Operating:
[tex]f(-b)=(-b+c)^2-(b-c)[/tex]
The value of f(-b) is not zero. This means Eunju is right, x+b is not a factor of f(x).
Part 2:
We must find out if [tex]x^2+5x+6[/tex] is a factor of [tex]x^4+5x^3+2x^2-20x-24[/tex] without using long division or synthetic division.
We can use the polynomial remainder theorem again, but since the factor is not in the form (x-a), we can factor it as follows:
[tex]x^2+5x+6 =(x+2)(x+3)[/tex]
Now we just apply the theorem twice. If both remainders are zero, then the assumption is true.
Let's make:
[tex]f(x)=x^4+5x^3+2x^2-20x-24[/tex]
Find f(-2):
[tex]f(-2)=(-2)^4+5(-2)^3+2(-2)^2-20(-2)-24[/tex]
[tex]f(-2)=16-5*8+2*4+40-24 =16-40+8+40-24=0[/tex]
Find f(-3):
[tex]f(-3)=(-3)^4+5(-3)^3+2(-3)^2-20(-3)-24[/tex]
[tex]f(-3)=81-5*27+2*9+60-24[/tex]
[tex]f(-3)=81-135+18+60-24 =0[/tex]
Since both f(-2) and f(-3) are zero, [tex]x^2+5x+6[/tex] is a factor of [tex]x^4+5x^3+2x^2-20x-24[/tex].
