In the plane rectangular coordinate system, the symbol of the point coordinates in the first quadrant is (positive, positive); The symbol of the coordinates of the second quadrant is (negative, positive); The symbol of the coordinates of the third quadrant point is (negative, negative); The dot symbols in the fourth quadrant are (positive, negative). So knowing the symbol of a point coordinate can tell which quadrant it is in. The point (x, 0) is on the X axis, and the point (0, y) is on the axis.

The understanding of the sign looking at the quadrant: parity is unchanged, and then the sign looking at the quadrant, for the trigonometric function value of kπ/2 α (k ∈ z). When k is even, you will get the function value of α with the same name. Even if the function name remains the same, when k is odd, you will get the corresponding cofunction value of α, that is, sin→cos；; ; cos→sin； Tan → Kurt; Canvas bed → tan.

The trigonometric function value of any angle in the first quadrant is "+",then only sine and internal cotangent in the second quadrant are "+",and the rest are "-". In the third quadrant, only the tangent and cotangent functions are "+",and then the chord function is "-". In the fourth quadrant, only cosine and secant are "+",and the rest are "-".

Positive and negative formulas of trigonometric function quadrant;

1, the abscissa of a quadrant is positive and the ordinate is positive; The abscissa of the two quadrants is negative and the ordinate is positive; The abscissa of the three quadrants is negative and the ordinate is negative; The abscissa of the four quadrants is positive and the ordinate is negative. Positive and negative formulas of four-quadrant trigonometric function: one is all positive; Two sine (cotangent); Cut in twos and threes; Four cosines (secant).

2. The presentation format is "Quadrant"/"+or-". Sine function: y=sinx, one/+,two/+,three/-,four/-; Cosine function: y=cosx, one/+,two/-,three/-,four/+; Tangent function: y=tanx, one/+,two/-,three/+,four/-; Cotangent function: y=cotx, one/+,two/-,three/+,four/-.