Odd couples, symbols look at quadrants.

The symbols on the right side of the formula are angles k 360+α (k ∈ z),-α, 180 α, and when α is regarded as an acute angle, it is 360-α.

The sign of the original trigonometric function value in the quadrant can be remembered.

The name of horizontal induction remains unchanged; Symbols look at quadrants.

How to judge the symbols of various trigonometric functions in four quadrants, you can also remember the formula "a full pair; Two sinusoids; The third is cutting; Four cosines ".

The meaning of this 12 formula is:

The four trigonometric functions at any angle in the first quadrant are "+";

In the second quadrant, only the sine is "+",and the rest are "-";

The tangent function of the third quadrant is+and the chord function is-.

In the fourth quadrant, only cosine is "+",others are "-".

The above memory formulas are all positive, sine, tangent and cosine.

★ Inductive formula ★

Commonly used inductive formulas have the following groups:

Formula 1:

Let α be an arbitrary angle, and the values of the same trigonometric function with the same angle of the terminal edge are equal:

sin(2kπ+α)=sinα

cos(2kπ+α)=cosα

tan(2kπ+α)=tanα

cot(2kπ+α)=cotα

Equation 2:

Let α be an arbitrary angle, and the relationship between the trigonometric function value of π+α and the trigonometric function value of α;

Sine (π+α) =-Sine α

cos(π+α)=-cosα

tan(π+α)=tanα

cot(π+α)=cotα

Formula 3:

Arbitrary angle α sum

Relationship between trigonometric function values of-α:

Sine (-α) =-Sine α

cos(-α)=cosα

tan(-α)=-tanα

Kurt (-α) =-Kurt α

Equation 4:

The relationship between π-α and the trigonometric function value of α can be obtained by Formula 2 and Formula 3:

Sine (π-α) = Sine α

cos(π-α)=-cosα

tan(π-α)=-tanα

cot(π-α)=-coα