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Question

If α and β are the zeros of the quadratic polynomial f(x)=x21, find a quadratic polynomial whose zeros are 2αβ and 2βα

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Solution

Given the polynomial,
f left parenthesis x right parenthesis equals x squared minus 1
and the roots of the polynomial are alpha space a n d space beta.
Hence the sum of zeros = -b/a
And product of zeros = c/a
Here, a=1, b=0 and c=-1.
alpha plus beta equals 0 over 1 equals 0 space.... space i right parenthesis
alpha beta equals negative 1 space.... space i i right parenthesis

Now, If the zeros of the polynomial are fraction numerator 2 alpha over denominator beta end fraction space a n d space fraction numerator begin display style 2 beta end style over denominator begin display style alpha end style end fraction

So, the sum of zeros= -4fraction numerator 2 alpha over denominator beta end fraction plus fraction numerator 2 beta over denominator alpha end fraction equals fraction numerator 2 alpha squared plus 2 beta squared over denominator alpha beta end fraction equals fraction numerator 2 left parenthesis alpha squared plus beta squared right parenthesis over denominator alpha beta end fraction equals fraction numerator 2 left parenthesis alpha squared plus beta squared plus 2 alpha beta minus 2 alpha beta right parenthesis over denominator alpha beta end fraction equals fraction numerator 2 left parenthesis left parenthesis alpha plus beta right parenthesis squared minus 2 alpha beta right parenthesis over denominator alpha beta end fraction equals fraction numerator 2 left parenthesis 0 squared minus 2 left parenthesis negative 1 right parenthesis right parenthesis over denominator negative 1 end fraction equals negative 4
Again, the product of the zeroes
left parenthesis fraction numerator 2 alpha over denominator beta end fraction right parenthesis left parenthesis fraction numerator 2 beta over denominator alpha end fraction right parenthesis equals 4

Now the required quadratic equation is;

K(x2(sum of zeroes)x+(product of zeroes)

K(x2+4x+4)=0


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