The answer would be D. It is true, because the cosine function has a period of 2[tex] \pi [/tex]
Cosine function has period of 2[tex] \pi [/tex] because the function value will be same for variable that 2[tex] \pi [/tex] appart. In the problem, cos [tex]- \pi /2[/tex] and cos [tex] 3 \pi /2 [/tex] difference would be 4[tex] \pi [/tex], which is 2 * [tex] 2 \pi [/tex]. That means they both should have same value.
