Question

which of the following expresses the possible number of positive real solutions for the polynomial equation shown below

Answer 1

The polynomial equation x³ - 4x² - 7x + 28 = 0, has solutions -√7, √7, and 4, among which √7 and 4 are positive real solutions. Hence we have two positive real solutions. Hence, option D is the right choice.

In the question, we are asked for the number of positive real solutions for the polynomial equation, x³ - 4x² - 7x + 28 = 0.

To find the solutions, we do as follows:

x³ - 4x² - 7x + 28 = 0,

or, (x³ - 7x) - (4x² + 28) = 0 {Grouping},

or, x(x² - 7) - 4(x² - 7) = 0 {Taking common},

or, (x - 4)(x² - 7) = 0 {Grouping},

or, (x - 4)(x + √7)(x - √7) = 0 {Using the formula: $a^2 - b^2 = (a+b)(a-b)$}.

By the zero-product rule, the solutions are:

x - 4 = 0, or, x = 4,

x + √7 = 0, or, x = -√7,

x - √7 = 0, or, x = √7.

Thus, the positive real solutions are 4, and √7. Hence, there are two positive real solutions.

Thus, the polynomial equation x³ - 4x² - 7x + 28 = 0, has solutions -√7, √7, and 4, among which √7 and 4 are positive real solutions. Hence we have two positive real solutions. Hence, option D is the right choice.

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The complete question is:

"Which of the following expresses the possible number of positive real solutions for the polynomial equation shown below?

x³-4x²-7x+28=0

a. two or zero

b. three or one

c. one

d. two"