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Questions  

 Let the function f:RR be defined by f(x)=2x+sinx for xR . Then f is 

a
one-to-one and onto
b
one-to-one but not onto
c
onto but not one-to-one
d
neither one-to-one nor onto

detailed solution

Correct option is A

Given that f(x)=2x+sin⁡x,x∈R or  f′(x)=2+cos⁡x But −1≤cos⁡x≤1 or  1≤2+cos⁡x≤3∴ f′(x)>0∀x∈R Therefore, f(x) is strictly increasing and, hence, one-one.   Also, as x→∞,f(x)→∞, and x→−∞,f(x)→−∞ . Therefore,  Range of f(x)=R=co-domain⁡ of f(x) Hence, f(x) is onto.  Thus, f(x) is one-one and onto.

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Similar Questions

Which of the following statements are incorrect?

 I. If f(x) and g(x) are one-one then f(x)+g(x) is also one-one

 II. If f(x) and g(x) are one-one then f(x)g(x) is also one-one

 III. If f(x) is odd then it is necessarily one-one. 


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