Trigonometric function remembers the definition ratio of jingle triangle, and radian is fused with real number;
Three kinds of good induction have twice the difference in flexibility at the same angle.
If there are three equilibria before the solution, there will be a pulse after the solution;
The calculation of angle value is big or small, and the tangent of chord line meets differently.
Trigonometric function remembers odd and even formulas, and symbols look at quadrants.
"Odd, even" refers to the parity of a multiple of π/2, and "variable, constant" refers to the change of the name of a trigonometric function: "variable" refers to the change of sine into cosine and tangent into cotangent. (and vice versa) The meaning of "symbol looking at quadrant" is: take angle α as an acute angle, regardless of the quadrant where angle α is located, look at what quadrant angle N (π/2) α is, and then get whether the right side of the equation is positive or negative.
Take cos(π/2+α)=-sinα as an example. In cos(π/2+α) on the left of the equation, n= 1, so the symbol on the right is sinα, and α is regarded as an acute angle, so π/2.