Determine whether the following functions are bijective.(a) f : R → R, with y = f (x) = 3x + 52(b) f : R → R, with y = f (x) = (2x − 7)2(c) f : R → R, with y = f (x) = √3x − 1
Question
Determine whether the following functions are bijective.(a) f : R → R, with y = f (x) = 3x + 52(b) f : R → R, with y = f (x) = (2x − 7)2(c) f : R → R, with y = f (x) = √3x − 1
Solution
(a) The function f(x) = 3x + 52 is bijective. It is injective (one-to-one) because for every x1 ≠ x2, we have f(x1) ≠ f(x2). It is surjective (onto) because for every y in R, there exists an x in R such that f(x) = y.
(b) The function f(x) = (2x - 7)^2 is not bijective. It is not injective because for x1 ≠ x2, we can have f(x1) = f(x2). For example, f(3) = f(5) = 4. It is not surjective because for y < 0 in R, there does not exist an x in R such that f(x) = y.
(c) The function f(x) = √(3x - 1) is not bijective. It is injective because for every x1 ≠ x2, we have f(x1) ≠ f(x2). However, it is not surjective because for y < 0 in R, there does not exist an x in R such that f(x) = y.
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