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Question

If α and β are the zeros of the quadratic polynomial f(x)=x23x2, find a quadratic polynomial whose zeros are 12α+β and 12β+α

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Solution

If alpha and betaare the roots of space x squared minus 3 x minus 2 equals 0
then alpha+beta=3 and alphabeta = -2

So the equation with roots as fraction numerator 1 over denominator 2 alpha plus beta end fraction space a n d space fraction numerator 1 over denominator 2 beta plus alpha end fraction space w i l l space b e
Sum of roots = fraction numerator 1 over denominator 2 alpha plus beta end fraction+fraction numerator 1 over denominator 2 beta plus alpha end fraction space=
fraction numerator 2 beta plus alpha plus 2 alpha plus beta over denominator 5 alpha beta plus 2 left parenthesis alpha squared plus beta squared right parenthesis end fraction equals fraction numerator 3 left parenthesis alpha plus beta right parenthesis over denominator 5 alpha beta plus 2 left curly bracket left parenthesis alpha plus beta right parenthesis squared minus 2 alpha beta right curly bracket end fraction equals fraction numerator begin display style 3 left parenthesis alpha plus beta right parenthesis end style over denominator begin display style alpha beta plus 2 left parenthesis alpha plus beta right parenthesis squared end style end fraction equals fraction numerator begin display style 3 left parenthesis 3 right parenthesis end style over denominator begin display style negative 2 plus 2 left parenthesis 3 right parenthesis squared end style end fraction equals 9 over 16

Product of roots = (fraction numerator 1 over denominator 2 alpha plus beta end fraction)(fraction numerator 1 over denominator 2 beta plus alpha end fraction space) = fraction numerator 1 over denominator 5 alpha beta plus 2 left parenthesis alpha squared plus beta squared right parenthesis end fraction equals fraction numerator 1 over denominator 5 alpha beta plus 2 left curly bracket left parenthesis alpha plus beta right parenthesis squared minus 2 alpha beta right curly bracket end fraction equals fraction numerator begin display style 1 end style over denominator begin display style alpha beta plus 2 left parenthesis alpha plus beta right parenthesis squared end style end fraction equals fraction numerator begin display style 1 end style over denominator begin display style negative 2 plus 2 left parenthesis 3 right parenthesis squared end style end fraction equals 1 over 16

Equation =
x squared minus 9 over 16 x plus 1 over 16 equals 0 o r 16 x squared minus 9 x plus 1 equals 0





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