Calculator question.

Whats is the minimum window that allows r^2=4cos (2theta)

multiple choice

A. [0,2pi]

B. [0, pi]

C. [-2pi, 2pi]

D [0, pi/2]

D. [0, pi/2]

Step-by-step explanation:

when Ф = 0 in radian

r² = 4cos (2 (0))

r² = 4 * 1

r² = 4

∴ r = √4 = 2

r = 2.

when Ф = π/2 in radian

r² = 4cos (2 (π/2))

r² = 4 * - 1

r² = - 4

∴ r = 0