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Prove that the function f(x)=cosx is str...

Prove that the function `f(x)=cosx` is strictly increasing in `(pi,\ 2pi)`

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We have given
`f(x)=cosx`
`f′(x)=−sinx`
As ,
`x in(pi,2pi)`
`impliessinx`<`0`
`implies−sinx`>`0`
`impliesf′(x)`>`0`
...
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RD SHARMA-INCREASING AND DECREASING FUNCTION -Solved Examples And Exercises
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  2. Prove that the function f(x)=cosx is strictly decreasing in (0,\ pi)

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  3. Prove that the function f(x)=cosx is strictly increasing in (pi,\ 2pi)

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