no, if you add a triangle into a unit circle with the top angle being 21, and the bottom angle being 69,  and we add a b and c to the sides, sin (21) would be the opposite of a or the hypotenuse of c. and the cos sign of the 69 degrees is gonna be adjacent a over the hypotenuse c, so they are both a over c so sin (21) is = to cos (69). if we were to rotate the 69 degree angle all the way around the circle once and get back to the original spot, it would be 69 + 360 which is cos (429). if we go around twice and add 360 to 429, it would be cos (789) therefore, the joke here is sin (21) = cos (789).