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Find all the zeroes of polynomial 2x4

– 9x3 + 5x2 + 3x – 1 ,if two of its zeroes are 2 + √3 & 2 - √3

User Lulop
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Answer:

x ∈ {-1/2, 1, 2-√3, 2+√3}

Explanation:

The given zeros mean that one of the quadratic factors of the given polynomial is ...

(x -2)^ -3 = x^2 -4x +1

When that is factored out (see first attachment), the remaining quadratic is ...

2x^2 -x -1

This can be factored as ...

= (2x +1)(x -1)

which has roots that make these factors zero: x = -1/2, x = 1.

So, all of the zeros of the given polynomial are ...

-1/2, 1, 2-√3, 2+√3 . . . all zeros

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A graphing calculator can often point to the zeros of the function quite nicely.

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Additional comments

When p is a zero of a polynomial, (x-p) is a factor of it. The given zeros mean that factors are (x-2-√3) and (x-2+√3). The product of these factors is the difference of the squares (x-2)^2 and (√3)^2, so is (x -2)^2 -3.

Using the pattern for the square of a binomial, we see this is ...

(x-2)^2 = x^2 -2·2x +2^2 = x^2 -4x +4

The product of the given factor is then 3 subtracted from this square. The given zeros mean there is a quadratic factor of ...

(x-2-√3)(x-2+√3) = (x-2)^2 -3 = x^2 -4x +4 -3 = x^2 -4x +1

Find all the zeroes of polynomial 2x4 – 9x3 + 5x2 + 3x – 1 ,if two of its zeroes are-example-1
Find all the zeroes of polynomial 2x4 – 9x3 + 5x2 + 3x – 1 ,if two of its zeroes are-example-2
User Barbecu
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5.4k points