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Total number of integral values of a such that `x^2 + ax + a + 1 = 0` has integral roots is equal to : (A) one 45. (B) two (C) three (D) fourA. oneB. twoC. threeD. four |
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Answer» Correct Answer - B If `x^(2) + ax + a + 1 = 0` has integral roots. Then, ist discriminant must be a perfect square. `therefore" "a^(2) - 4a - 4 = lambda^(2), "where" lambda in Z`. `rArr" "(a-2)^(2)-lambda^(2) = 8` `rArr" "(a-2+lambda)(a-2-lambda)=8` `rArr" "a-2+lambda = 4 and a - 2 - lambda = 2` `or," "a-2+lambda =2 and a-2-lambda = 4` `or," "a-2+lambda=-4 and a-2-lambda = -2` `or," "a-2+lambda = -2 and a-2 - lambda = -4` `rArr" "(a=5, lambda=1)or, (a=5, lambda =-1)or, (a =-1, lambda = -1)or, (a = -1, lambda = 1)` Thus, there are only two integral values of a viz 5 and -1. |
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