Construct a polynomial function with the stated properties calculator

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at x=
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Question 1119081: Construct a polynomial function with the stated properties. Reduce all fractions to lowest terms.
Third-degree, with zeros of −3, −2, and 1, and passes through the point (3,9).

Found 2 solutions by josgarithmetic, MathTherapy:Answer by josgarithmetic(37585)  
(Show Source):
Answer by MathTherapy(10131)   (Show Source):

You can put this solution on YOUR website!

Construct a polynomial function with the stated properties. Reduce all fractions to lowest terms.
Third-degree, with zeros of −3, −2, and 1, and passes through the point (3,9).

<======= INCORRECT, so IGNORE, as usual. I'll give you a hint:


The general 3rd degree polynomial is f(x) = ax3 + bx2 + cx + d

Or in factored form, it would be f(x) = a(x-r)(x-s)(x-t), where r, s and t are roots of the polynomial equation.

So you have f(x) = a(x+3)(x+1)(x-2)

Use the point (1,11) to plug in and solve for a.

f(1) = 11 = a(1+3)(1+1)(1-2)

11 = a(4)(2)(-1)

11 = a(-8)

a = -11/8

Thus f(x) = -(11/8)(x+3)(x+1)(x-2) = -(11/8)(x+3)(x2 - x -2)

f(x) = -(11/8)(x3 - x2 - 2x + 3x2 - 3x + 6) = -(11/8)(x3 + 2x2 - 5x + 6)

f(x) = -11x3 /8 - 11x2 /4 + 55x/8 - 33/4

  • #1

Pretty lost on this.

"Construct a polynomial function with the stated properties. Reduce all fractions to lowest terms.:

Third-degree, with zeros of -2,-1, and 3, and passes through the poing (4,12)"

(Happy)

  • #2

Pretty lost on this.

"Construct a polynomial function with the stated properties. Reduce all fractions to lowest terms.:

Third-degree, with zeros of -2,-1, and 3, and passes through the poing (4,12)"

(Happy)

If \(\displaystyle x = \alpha\) is a zero then \(\displaystyle (x - \alpha)\) is a factor. So \(\displaystyle y = k(x + 2)(x + 1)(x - 3)\).

Now substitute (4, 12) and solve for k.

Vanessa J.

asked • 04/06/22

Construct a polynomial function with the stated properties. Reduce all fractions to lowest terms. Third-degree, with zeros of −2, −1, and 3, and passes through the point (4,6

1 Expert Answer

Scott B. answered • 04/06/22

Education focused Physics Professor

Let's start with the zeros part.

If a polynomial p(x) has a zero at some particular value like 3, it means that the binomial (x-3) is one of its factors. Meaning, we can write it as p(x)=(x-3)g(x), where g(x) is some further polynomial expression. Since we're actually given three zeros here, we can write p(x)=(x+2)(x+1)(x-3)g(x), where again, g(x) is some further polynomial expression we have yet to find. You can check that x=-2, x=-1, and x=3 all cause this expression to be 0.

Now we use the fact that we're looking for a third degree polynomial. This tells us that, in fact, g(x) is at most some constant (that I'll now relabel a), because (x+2)(x+1)(x-3) is ALREADY a third degree polynomial. If g(x) contains any factors of x, it will raise us to a fourth order polynomial or higher. So, p(x)=a(x+2)(x+1)(x-3), where a is some constant.

To find what a is, we use the last given information, that the curve must pass through the point (4,6). Substituting 4 in for x, we get

p(4)=a(4+2)(4+1)(4-3)=a(6)(5)(1)=30a=6

So, a=6/30, or 1/5

In total, we have

p(x)=(1/5)(x+2)(x+1)(x-3)

You may expand this out if you prefer.

p(x)=(1/5) x3 - (7/5) x - 6/5

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