JEE Main 2019 Mathematics question
Let the numbers 2, b, c be in an A.P. and . If det(A) ∈ [2, 16], then c lies in the interval:
Answer: (B)
Solution
Vandermonde: det = (b − 2)(c − 2)(c − b) = ∈ [2, 16] ⇒ d ∈ [1, 2] ⇒ c = 2 + 2d ∈ [4, 6].
Let the numbers 2, b, c be in an A.P. and . If det(A) ∈ [2, 16], then c lies in the interval:
Vandermonde: det = (b − 2)(c − 2)(c − b) = ∈ [2, 16] ⇒ d ∈ [1, 2] ⇒ c = 2 + 2d ∈ [4, 6].