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If the equation `x^(4)-4x^(3)+ax^(2)+bx+1=0` has four positive roots, fond the values of a and b. |
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Answer» Let `x_(1),x_(2),x_(3),x_(4),` are the roots of the equation `x_(1)x_(1)x_(1)x^(4)-4x^(3)+ax^(2)+bx+1=0 " " "....(i)"` `:.x_(1)+x_(2)+x_(3)+x_(4)=4 " and "x_(1)x_(2)x_(3)x_(4)=1` `:.AM=(x_(1)+x_(2)+x_(3)+x_(4))/(4)=(4)/(4)=1` and `GM=(x_(1)x_(2)x_(3)x_(4))^((1)/(4))=1` `i.e., AM=GM` which is true only when `x_(1)=x_(2)=x_(3)=x_(4)=1` Hence, given equation has all roots identical, equal to i.e., equation have form `(x-1)^(4)=0` `implies x^(4)-4x^(3)+6x^(2)-4x+1=0" " "....(ii)"` On comparing Eqs. (i) and (ii), we get `a=6,b=-4`. |
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