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If `alpha, beta` are roots of the equation `2x^2 + 6x + b = 0 (b < 0),` then `alpha/beta+beta/alpha` is less thanA. 2B. -2C. 18D. none of these |
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Answer» Correct Answer - B We have, `alpha+beta = -3 and alpha beta = (b)/(2)` Since b `lt` 0, therefore discriminant `D = 36 - 4b gt 0`. So, `alpha and beta` are real. Now, `(alpha)/(beta)+(beta)/(alpha)=(alpha^(2)+beta^(2))/(alpha beta)=((alpha+beta)^(2)-2 alpha beta)/(alpha beta)=((alpha+beta)^(2))/(alpha beta)-2=(18)/(b)-2` `rArr" "(alpha)/(beta) + (beta)/(alpha) lt -2" "[because b lt 0]` ALITER We have, `alpha beta = (b)/(2) lt 0` `therefore" "alpha and beta` are of opposite signs `rArr" "(alpha)/(beta) lt 0` `rArr" "(alpha)/(beta)+(beta)/(alpha) lt - 2" "[because x + (1)/(x) lt - 2 "for all x" lt 0, x ne -1]` |
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