1.

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

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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