1.

The domain of definiton of the function `f(x)=(1)/(sqrt(x^(12)-x^(9)+x^(4)-x+1))` , isA. `(-oo,-1)`B. `(1,oo)`C. `(-1,1)`D. R

Answer» Correct Answer - D
f(x) assumes real values , if
`x^(12)-x^(9)+x^(4)-x+1 gt0`
`implies (x^(12)+x^(4))-(x^(9)+x)+1) gt 0`
`implies x^(4)(x^(8)+1)-x(x^(8)+1)+1 gt 0`
`implies x(x^(8)+1) (x^(3)-1)+1 gt 0`
Clearly , it is true for all ` x ge 1 or , x le 0`.
For ` 0 lt x lt 1`, we have
`x^(4) gt x^(8)`
`implies x^(4)+1 gt x^(8)+1`
`implies x^(4)+1 gt x(x^(8)+1)`
`implies -x(x^(8)+1)+x^(4)+1 gt 0`
`implies x^(12)-x(x^(8)+1)+x^(4)1 gt 0`
Thus , `x^(12)-x^(9)+x^(4)-x+1 gt 0` for all ` x in R. `
Hence domain of f(x) is R.


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