Question

Which of the following expresses the possible number of positive real solutions for the polynomial equation x^3-4x^2-7x+28=0

A. Two or zero
B. Two
C. One
D. Three or one

Answer 1

x^3- 4x^2 - 7x + 28 = 0
x^2(x - 4) - 7(x - 4) = 0
(x^2 - 7) (x - 4) = 0
x^2 - 7 = 0; x = + - √7
x - 4 = 0; x = 4

answer is D. Three or one

Answer 2

A. Two or zero

Explanation:

Descartes' rule of signs show that there are either 2 or 0 positive real roots