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math question here....please help?

assume that x-2 is a factor of the polynomial f(x)=x^3+ax^2+bx+2 and that f(x) gives a remainder of -3 when it is divided by x+1. Then a=?,b=?

Update:

i don't understand the second part. why is dividing f(x) by (x+1) which gives a -3 remainder becomes f(-1)=-3?

2 Answers

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  • 1 decade ago
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    If (x-2) is a factor of f(x) then by the Factor Theorem, f(2)=0.

    If f(x) gives a remainder of -3 when divided by (x+1) then by the Remainder Theorem, f(-1)=-3. So, pluggining in:

    8+4a+2b+2 = 0 [f(2)= 0]

    -1+a-b+2 = -3 [f(-1)= -3]

    which gives the system of equations

    4a+2b=-10

    a - b= -4

    The solution to this is a = -3, b = 1

  • 1 decade ago

    If a binomial is a factor of the polynomial, that means that +2 in x's place will make the polynomial =0. This will be the first equation - your variables will be a & b.

    The second equation comes from the other fact that you get a remainder after dividing by x+1. So, -1 in x's place will make the polynomial equal -3.

    Now you have 2 equations with 2 variables - a & b. Do some simplifying of the equations (get a & b terms on one side), then solve the system of equations using either substitution methods or the addition (elimination) method.

    Good Luck! :-)

    Source(s): Math teaching for 21 years!
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