Standard formula sin (kπ/2+/-x) or cos (kπ/2+/-x).
"Even constant of odd variables" means that if the parameter k is odd, sine becomes cosine and cosine becomes sine; If k is even, it keeps the same sine and cosine as the original formula. The meaning of "symbol looking at quadrant" is: assuming that X is an acute angle, if the original formula is negative, a negative sign should be added in front of the finally converted formula; If it is positive, there is no need to add a symbol before the final transformed formula.
Extended data:
In the plane rectangular coordinate system, four areas divided by horizontal axis and vertical axis are divided into four quadrants. The quadrant takes the origin as the center and the X axis and Y axis as the dividing line. The upper right is called the first quadrant, the upper left is called the second quadrant, the lower left is called the third quadrant, and the lower right is called the fourth quadrant. The points on the coordinate axis do not belong to any quadrant.
The first quadrant: (positive+,+positive), the abscissa and ordinate have the same sign, and it is denoted as xy>0; The second quadrant: (negative-,+positive), which has different symbols in horizontal and vertical coordinates and is expressed as xy.