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Question -

Show that f(x) = x9┬а+ 4x7┬а+11 is an increasing function for all x┬а╧╡┬аR.



Answer -

Given f (x) = x9┬а+ 4x7┬а+ 11

Now by differentiating above equation with respect to x, we get

тЗТ┬а

тЗТ┬аfтАЩ(x)= 9x8┬а+ 28x6

тЗТ┬аfтАЩ(x)= x6(9x2┬а+ 28)

As given x┬а╧╡┬аR

тЗТ┬аx6┬а>0 and 9x2┬а+ 28 > 0

тЗТ┬аx6┬а(9x2┬а+28) > 0

тЗТ┬аfтАЩ(x)> 0

Hence, condition for f(x) to be increasing

Thus f(x) is increasing on interval x┬атИИ┬аR

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