I'm starting to dislike math

The ratio pv to nrt is plotted against pressure for ch4 at 0°c and 200°c. why does the curve for 0°c drop below the horizontal line for an ideal gas whereas the curve for 200°c does not?

Which best explains why this triangle is or is not a right triangle?

If cos(2x) = tan^2(y), show that cos(2y) = tan^2(x).