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Question

If ⎪ ⎪ ⎪⎪ ⎪ ⎪[2(sinxsinnx)+|sinxsinnx|2(sinxsinnx)|sinxsinnx|],xπ23,x=π2 where [x] denotes the integral part of x and x(0,π) and n>1
Show that f(x) is continuous and differentiable at x=π2.

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Solution

We have
f(x)=[2(sinxsinnx)+|sinxsinnx|2(sinxsinnx)|sinxsinnx|];xπ2

f(x)=3;x=π6
Ifx(0,π)andn>1
thensinxsinnx
So,
L.H.S=limx0f(π2h)f(π2)h

=limx0[2(sinhsinnh)+sinhsinnh2(sinhsinnh)|sinhsinnh|]3h

=limx0[2(sinhsinnh)+sinhsinnh2(sinhsinnh)|sinhsinnh|]3h[cancle(sinhsinnh)]

=limx0[2+121]3h=limx0[3]3h=limx00h=0

Now,
R.H.S=limx0f(π2+h)f(π2)h

=limx0[2(sinhsinnh)+sinhsinnh2(sinhsinnh)|sinhsinnh|]3h

=limx0[2(sinhsinnh)+sinhsinnh2(sinhsinnh)+|sinhsinnh|]3h[cancle(sinhsinnh)]

=limx0[2+121]3h=limx0[3]3h=limx00h=0
So, L.H.S=R.H.S=0(finite)
So, f(n) is differentiable at x=π2 and also continous.

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