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Which of the following statements are true?

(A) f:R→Rf:\mathbb{R} \to \mathbb{R} given by f(x)=3xf(x) = 3x is one-one onto.

(B) f:R→Rf:\mathbb{R} \to \mathbb{R} given by f(x)=x4f(x) = x^4 is one-one and onto.

(C) f:Z→Zf:\mathbb{Z} \to \mathbb{Z} given by f(x)=x2f(x) = x^2 is neither one-one nor onto.

(D) f:R→Rf:\mathbb{R} \to \mathbb{R} given by f(x)=∣x∣f(x) = |x| is neither one-one nor onto.

(Where R\mathbb{R} is the set of all real numbers and Z\mathbb{Z} is the set of all integers)

Choose the correct answer from the options given below:

Solution

✅ Correct Option: 3

A: f(x)=3xf(x)=3x is bijective on R\mathbb{R}, true. B: x4x^4 has f(1)=f(−1)f(1)=f(-1), not one-one, also range is [0,∞)[0,\infty), not onto, false. C: x2x^2 on Z\mathbb{Z} is not one-one nor onto, true. D: ∣x∣|x| on R\mathbb{R} is not one-one nor onto, true. So A, C, D.

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