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Show that f(x)=cos(2x+pi//4) is an incre...

Show that `f(x)=cos(2x+pi//4)` is an increasing function on `(3pi//8,\ 7pi//8)` .

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We have `f(x)=cos(2x+π/4​)`
`dy/dx​=−2sin(2x+π/4​)`
Since,` 3π/8 ​< x < 7π/8`
​ ⇒`3π/4​<2x<7π/4`
​ ⇒`π<2x+π/4​<2π`
...
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