cos(-α)= cosα；

sin(π/2-α)= cosα；

cos(π/2-α)= sinα；

sin(π/2+α)= cosα；

cos(π/2+α)=-sinα；

sin(π-α)= sinα；

cos(π-α)=-cosα；

sin(π+α)=-sinα；

cos(π+α)=-cosα；

tanA = sinA/cosA；

tan(π/2+α)=-cotα；

tan(π/2-α)= cotα；

tan(π-α)=-tanα；

tan(π+α)=tanα

Simplify and evaluate the knowledge reserve needed for trigonometric function of extended data;

(1) Memorize the trigonometric function value of a specific angle;

② Pay attention to the flexible application of inductive formulas;

③ The requirements of trigonometric function simplification are the least number of terms, the least number of times, the least function name, the simplest denominator and the best evaluation.

The meaning of the inductive formula formula "even if it changes strangely, the symbol will look at the quadrant";

Trigonometric function value of k × π/2 A (k ∈ z).

(1) When k is an even number, it is equal to the trigonometric function value of the same name of α, and a symbol is added in front to indicate the original trigonometric function value when α is regarded as an acute angle;

(2) When k is an odd number, different trigonometric function values equal to α are preceded by a sign of the original trigonometric function value when α is regarded as an acute angle.

References:

Baidu Encyclopedia-formulas of trigonometric functions