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if alpha, beta are the roots of the quadratic equation ax^2+bx+c=0 find a quadratic equation whose roots are alpha^2+beta^2 and aloha^-2+beta^-2 |
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Answer» Answer: a²c²x² - ( b^2 - 2ac )( a^2 + c^2 )x + ( b^2 - 2ac )^2 = 0 Step-by-step explanation: Eq. is ax^2 + bx + c = 0 ⇒ x^2 - (-b/a)x + (c/a) = 0. Quadratic equation written in the form of x^2 - Sx + P = 0 represent S as sum of roots and P as the product of their roots. So, here if α and β are roots. S = α + β = - b / a P = αβ = c / a Therefore, α^2 + β^2 = (α+β)² - 2αβ = ( - b / a )^2 - 2( c / a ) = b^2 / a^2 - 2c / a = ( b^2 - 2ac ) / a^2 1 / α^2 + 1 / β^2 = ( α^2 + β^2 ) / ( αβ )^2 = {(b^2 - 2ac)/a^2}/{(c/a)^2} = ( b^2 - 2ac ) / c^2 Here, we are asked for the equation with roots ( b^2 - 2ac ) / a^2 and ( b^2 - 2ac ) / c^2. So, if that equation is x^2 - Kx + L = 0. So, K is the sum of roots and L is the product of roots. This means : K = ( b^2 - 2ac ) / a^2 + ( b^2 - 2ac ) / c^2 K = ( b^2 - 2ac )( a^2 + c^2 ) / ( ac )^2 And, L = ( b^2 - 2ac )/a^2 * ( b^2 - 2ac )/c^2 L = ( b^2 - 2ac )^2 / ( ac )^2
HENCE the REQUIRED equation is : x^2 - x( b^2 - 2ac )( a^2 + c^2 )/(ac)^2 + ( b^2 - 2ac )^2/(ac)^2 = 0 ⇒ a²c²x² - ( b^2 - 2ac )( a^2 + c^2 )x + ( b^2 - 2ac )^2 = 0 Hence the required equation is a²c²x² - ( b^2 - 2ac )( a^2 + c^2 )x + ( b^2 - 2ac )^2 = 0. |
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