If the sin 0° = 0, then which statement is true?

cos 90° = 1, because the cosine and sine are complements
cos 180° = 1, because the cosine and sine are supplements
cos 90° = 0, because the cosine and sine are complements
cos 180° = 0, because the cosine and sine are supplements

Np4=12np2 with clear explanation.

20 ! need which shows a difference of squares? 10y^2-4x^2 16y^2-x^2 8x^2-40x+25 64x^2-48x+9

In a certain pentagon, the interior angles are a,b,c,d,e where a,b,c,d,e are integers strictly less than 180. ("strictly less than 180" means they are "less than and not equal to" 180.) if the median of the interior angles is 61 and there is only one mode, then what are the degree measures of all five angles?