First slide
Theory of equations
Question

Let  α1,β1be the roots x26x+p=0 and α2,β2 be the roots of x254x+q=0. If α1,β1,α2,β2 from an increasing G.P., then the value of (q -p) is _________.

Moderate
Solution

Let α1=A,β1=AR,α2=AR2,β2=AR3
we have, α1+β1=6A(1+R)=6                       (1)
                 α1β1=pA2R=p                         (2)
Also, α2+β2=54AR2(1+R)=54           (3)
            α2β2=qA2R5=q                         (4)
Now, on dividing Eq. (3) by Eq. (1), we get
AR2(1+R)A(1+R)=546=9  or  R2=9
 R = 3 (as it is an increasing G.P.)
On putting R = 3 in Eq. (1), we get
A=64=32
 p=A2R=94×3=274 and q=A2R5=94×243=21874
Hence, qp=2187274=21604=540

 

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