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Questions  

f:RR defined by f(x)=12x|x|+cosx+1 is 

a
one-one and onto
b
one-one and into
c
many-one and onto
d
many-one and into

detailed solution

Correct option is A

fx = xx2+cosx+1    If x≥0 then fx = x22+cosx +1     f'x = x - sinx ≥0 for all x≥0  if x<0 then fx = -x22 + cosx +1 ⇒f'x=-x -sinx >0 since x is negative therefore f'x >0 for all x ∈R ⇒ f is increasing , hence f is one-one  and fx→∞ when x→∞ and fx→ -∞ when x→-∞  Range is = R ,    hence f is 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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