Alpha and bitter

Algebra Level 1

The roots of the equation x 2 6 x + 8 = 0 x^2 -6x +8 = 0 are α \alpha and β \beta . Find the equation whose roots are: α 2 \alpha^2 , β 2 \beta^2 ?

x 2 17 x + 34 x^2 - 17x + 34 =0 x 2 20 x + 64 x^2 - 20x + 64 =0 x 2 + 20 x 64 x^2 + 20x - 64 =0 x 2 + 2 x 3 x^2 + 2x -3 =0

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2 solutions

Sunil Pradhan
Jul 13, 2014

x² – 6x + 8 = 0 then (x – 4)(x – 2) = 0 then x = 4 or 2

for other equation x = 16 or x = 4 (square of roots of above equation

so equation is (x – 16)(x – 4) = 0 or x² – 2x + 64 = 0

It is simpler to use the Vieta's formulas to get that α β = 8 α 2 β 2 = 64 \alpha\beta= 8\implies \alpha^2\beta^2=64 , and there was only one option that had c = 64 c=64 .

mathh mathh - 6 years, 10 months ago
Hassan Raza
Jul 30, 2014

P 1 = α β = 8 1 = 8 N o w F i n d a n e q u a t i o n w h o s e r o o t s a r e α 2 & β 2 S u m o f r o o t s S 2 = α 2 + β 2 = α 2 + β 2 + 2 α β 2 α β = ( α + β ) 2 2 α β = ( S 1 ) 2 2 P 1 = 6 2 2 ( 8 ) = 36 16 S 2 = 20 P r o d u c t s o f r o o t s P 2 = α 2 β 2 = ( α β ) 2 = ( P 1 ) 2 = 8 2 P 2 = 64 T o f i n d E q u a t i o n , U s e t h i s f o r m u l a x 2 S x + p = 0 w e h a v e = > x 2 20 x + 64 = 0 a n s . . . . . . . . . . . { P }_{ 1 }=\alpha \beta =\frac { 8 }{ 1 } =8\\ Now\quad Find\quad an\quad equation\quad whose\quad roots\quad are\quad { \alpha }^{ 2 }\quad \& \quad { \beta }^{ 2 }\\ Sum\quad of\quad roots\\ { S }_{ 2 }={ \alpha }^{ 2 }+{ \beta }^{ 2 }={ \alpha }^{ 2 }+{ \beta }^{ 2 }+2\alpha \beta -2\alpha \beta ={ (\alpha +\beta ) }^{ 2 }-2\alpha \beta \\ ={ { ({ S }_{ 1 }) } }^{ 2 }-2{ P }_{ 1 }={ 6 }^{ 2 }-2(8)=36-16\\ \boxed { { S }_{ 2 }=20 } \\ Products\quad of\quad roots\\ { P }_{ 2 }={ \alpha }^{ 2 }{ \beta }^{ 2 }={ (\alpha \beta })^{ 2 }={ ({ P }_{ 1 }) }^{ 2 }={ 8 }^{ 2 }\\ \boxed { { P }_{ 2 }=64 } \\ To\quad find\quad Equation,\quad Use\quad this\quad formula\\ \boxed { { x }^{ 2 }-Sx+p=0 } \quad we\quad have\\ =>\quad \quad \qquad \qquad \boxed { { x }^{ 2 }-20x+64=0 } \quad ans...........\\

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