Let f be a real-valued function defined on the interval (0,∞) by f(x)=lnx+∫0x1+sintdt.
Then which of the following statement(s) is (are) true?
Answers:B. f′(x) exists for all x∈(0,∞) and f′ is continuous on (0,∞), but not differentiable on (0,∞) · C. there exists α>1 such that ∣f′(x)∣<∣f(x)∣ for all x∈(α,∞)
f(x)=lnx+∫0x1+sintdt,x∈(0,∞)If g(x)=∫0xh(t)dt then g′(x)=h(x)Check existence/continuity of f′,f′′; and bounds on ∣f∣,∣f′∣f′(x)=x1+1+sinx1+sinx=(sin2x+cos2x)21+sinx=sin2x+cos2xcorner where 1+sinx=0,i.e. x=23πf′ continuous but not differentiable at 23π⇒(1) FALSE,(2) TRUE∣f′(x)∣=x1+1+sinx≤1+2(x≥1)f(x)→∞(x→∞),f′ bounded⇒∣f′(x)∣<∣f(x)∣ for large x⇒(3) TRUEf(x)→∞⇒no β bounds ∣f(x)∣+∣f′(x)∣⇒(4) FALSETRUE statements: (2) and (3)f′(x)=x1+1+sinx;TRUE: (2),(3)