If α and β are the real roots of x2+px+q=0 and α4, β4 are the roots of x2−rx+s=0, then the equation x2−4qx+2q2−r=0 has always
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a
two real roots
b
two positive roots
c
two negative roots
d
roots of the opposite sign
answer is A.
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Detailed Solution
The given equation is x2+px+q=0 …. ( 1 ) α and β are the real roots of ( 1 )Then sum of the roots : α+β=−p, Product of the roots : αβ=q AndThe given another equation is x2−rx+s=0 …. ( 2 )α4, β4 are the roots of ( 2 )then sum of the roots : α4+β4=r, product of the roots : α4β4=s ∴ r>0. For the equation x2−4qx+2q2−r=0, Here a=1,b=−4q,c=2q2−r Dicriminant D=16q2−4(2q2−r)=8q2+4r>0 =8α2β2+4(α4+β4)=4(α2+β2)2 ⇒ equation has two real roots.