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Let `alpha and beta` be the roots of equation `px^2 + qx + r = 0 , p != 0`.If `p,q,r` are in A.P. and `1/alpha+1/beta=4`, then the value of `|alpha-beta|` is :A. `(sqrt(34))/(9)`B. `(2sqrt(13))/(9)`C. `(sqrt(61))/(9)`D. `(2sqrt(17))/(9)` |
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Answer» Correct Answer - B Since `alpha and beta` are roots of the the equation `px^(2)+qx+r=0`. Therefore, `alpha+beta = - (q)/(p) and alpha beta = (r)/(p)` Now, `(1)/(alpha)+(1)/(beta)=4 rArr (alpha+beta)/(alpha beta)=4 rArr -(q)/(r)=4 rArr q =-4r` It is given that p,q, r are in AP. Therefore, `2q = p+r rArr -8r = p+r rArr p = -9r` `therefore" "alpha + beta = -(q)/(p) = -(4)/(9) and alpha beta =(r)/(p) = -(1)/(9)` Now, `(alpha - beta)^(2) = (alpha+beta)^(2) - 4 alpha beta` `rArr" "(alpha-beta)^(2)=(16)/(81)+(4)/(9)=(52)/(81) rArr |alpha-beta|=(2 sqrt(13))/(9)` |
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