Engineering
Mathematics
Methods to Evaluate Limits
Maxima and Minima
Integration by Substitution
Question

Let f (x) = xcotxx+cotx where x(0,  π2) then

Limx0+   (xf(x))xxsinx is equal to  e6.

f (x) has exactly one point of local maxima in (0,  π2).

0π2f(x)dx  =  π2

f (x) has exactly one point of local minima in (0,  π2).

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Solution
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f(x)=x1+xtanx

now    f ' (x) = 1+xtanxx(xsec2x+tanx)(1+xtanx)2=1x2sec2x(1+xtanx)2=cos2xx2cos2x(1+xtanx)2

=(cosxx)(cosx+x)cos2x(1+xtanx)2=(cosxx)·  (cosx+x)cos2x(1+xtanx)2+ve

only one maxima in (0,  π2)