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Find the equation of a polynomial with given zeros: [tex]\(1\)[/tex] (multiplicity [tex]\(2\)[/tex]), [tex]\(2+\sqrt{2}\)[/tex], [tex]\(2-\sqrt{2}\)[/tex].

A. [tex]\(f(x)=x^4-7x^3+16x^2-14x+4\)[/tex]
B. [tex]\(f(x)=x^3-5x^2+6x-2\)[/tex]
C. [tex]\(f(x)=x^4+6x^3+11x^2+8x+2\)[/tex]
D. [tex]\(f(x)=x^4-6x^3+11x^2-8x+2\)[/tex]


Sagot :

To find the polynomial equation given its zeros, we will work through the problem step-by-step. The provided zeros are:

- 1 with a multiplicity of 2
- [tex]\(2 + \sqrt{2}\)[/tex]
- [tex]\(2 - \sqrt{2}\)[/tex]

## Step 1: Express zeros as factors of the polynomial

Given the zeros, the polynomial can be represented as:
[tex]\[ f(x) = (x - 1)^2 (x - (2 + \sqrt{2}))(x - (2 - \sqrt{2})) \][/tex]

## Step 2: Simplify the factors

First, we simplify [tex]\((x - 1)^2\)[/tex]:
[tex]\[ (x - 1)^2 = x^2 - 2x + 1 \][/tex]

Next, we simplify [tex]\((x - (2 + \sqrt{2}))(x - (2 - \sqrt{2}))\)[/tex]:
[tex]\[ (x - (2 + \sqrt{2}))(x - (2 - \sqrt{2})) = (x - 2 - \sqrt{2})(x - 2 + \sqrt{2}) \][/tex]
This is a difference of squares:
[tex]\[ = \left((x - 2) - \sqrt{2}\right)\left((x - 2) + \sqrt{2}\right) = (x - 2)^2 - (\sqrt{2})^2 = (x - 2)^2 - 2 \][/tex]

Simplify further:
[tex]\[ (x - 2)^2 - 2 = x^2 - 4x + 4 - 2 = x^2 - 4x + 2 \][/tex]

## Step 3: Multiply the simplified factors to find the polynomial

Now, we multiply the results from Step 2:
[tex]\[ (x^2 - 2x + 1)(x^2 - 4x + 2) \][/tex]

Use distributive property (FOIL method):
[tex]\[ (x^2 - 2x + 1)(x^2 - 4x + 2) = x^2(x^2 - 4x + 2) - 2x(x^2 - 4x + 2) + 1(x^2 - 4x + 2) \][/tex]

Distribute [tex]\(x^2\)[/tex]:
[tex]\[ x^2(x^2 - 4x + 2) = x^4 - 4x^3 + 2x^2 \][/tex]

Distribute [tex]\(-2x\)[/tex]:
[tex]\[ -2x(x^2 - 4x + 2) = -2x^3 + 8x^2 - 4x \][/tex]

Distribute [tex]\(1\)[/tex]:
[tex]\[ 1(x^2 - 4x + 2) = x^2 - 4x + 2 \][/tex]

Add all the expanded terms together:
[tex]\[ x^4 - 4x^3 + 2x^2 - 2x^3 + 8x^2 - 4x + x^2 - 4x + 2 \][/tex]

Combine like terms:
[tex]\[ x^4 - 6x^3 + 11x^2 - 8x + 2 \][/tex]

Therefore, the polynomial equation is:
[tex]\[ f(x) = x^4 - 6x^3 + 11x^2 - 8x + 2 \][/tex]

From the given options, the correct choice is:

D. [tex]\(f(x) = x^4 - 6x^3 + 11x^2 - 8x + 2\)[/tex]