Question 791551
Trigonometric functions cosine and sine are defined as the x and y coordinates of the point where the second side of the angle intersect the unit circle (a circle of radius 1, centered at the origin).
The angles are placed on the standard position of the first side coinciding with the positive x-axis, and angles are measured as the counterclockwise turn from the first side to the final side.
If you turn the positive x-axis counterclockwise {{{1&3/4}}} turns, that is a {{{360^o(7/4)=630^o}}}.
After that turn, the final side of the angle overlaps the negative y-axis, and intersects the unit circle at the point (0,-1), with {{{x=0}}}, {{{y=-1}}}, so {{{cos(630^o)=0}}} and {{{sin(630^o)=-1}}}.