Question

Express in radians the period of the graph of the equation y = 1/3(cox^2 x−sin^2 x).

Answer 1

between the typo and the font messup, it's hard to say
sin^2 and cos^2 has period pi (why not 2pi?)
cot^2 has period pi

So, I'd say whatever you have there has period pi

Answer 2

90 degree or pi in rad