Maths-
General
Easy

Question

For every x ε R, the polynomial x8 - x5 + x2 - x + 1 is :

  1. positive

  2. never positive

  3. positive as well as negative

  4. negative

hintHint:

In the given question, we are required to find the value of the polynomial x to the power of 8 minus x to the power of 5 plus x squared minus x plus 1 .

The correct answer is:

positive


    Step by step solution:
    Let f(x) = x to the power of 8 minus x to the power of 5 plus x squared minus x plus 1
    rightwards double arrowf(x) = x to the power of 5 left parenthesis x cubed minus 1 right parenthesis plus x left parenthesis x minus 1 right parenthesis plus 1
    rightwards double arrowf(x) = x to the power of 5 space left parenthesis space x minus 1 right parenthesis space left parenthesis x squared plus x plus 1 right parenthesisplus x left parenthesis x minus 1 right parenthesis space plus 1
    rightwards double arrowf(x) = x left parenthesis x minus 1 right parenthesisleft curly bracket x to the power of 4 left parenthesis x squared plus x plus 1 right parenthesis plus 1 right curly bracket plus 1
    x to the power of 4 greater or equal than 0 spaceand x squared plus x plus 1 greater or equal than 0
    CASE 1 : If x does not belong to (0,1)
    Then, f(x) greater than 0 [ since x left parenthesis x minus 1 right parenthesisgreater or equal than 0]
    CASE 2: If x space element of space left parenthesis 0 comma 1 right parenthesis , then f(x) > 0
    Thus, the polynomial is positive for all x element of R.
    Hence, option(c) is the correct option.

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