1.

Prove that the function f given byf(x) = log sin x" is increasing on ")0,pi/2) and decreasing on (pi/2,pi).

Answer»

Solution :f(X) = log (sin x)
` rArrf'(x) = (COS x)/(sin x) = cos x`
(a)f(x) is increasing.
` rArrf,(x) GT 0`
` rArrcot x gt 0`
`RARRX in (0,pi/2)`
`:.F(x)" is increasing in "(0,pi/2)`.
(b)f(x) is decreasing.
`rArrf'(x) lt 0`
` rArrcotx lt 0`
` rArrx in (pi/2, pi)`
` :. f(x)" is decreasing in "(pi/2, pi)`.


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