① Look at the quadrant.

② Positive and negative

(3) change the name to no.

Explain a little: all odd multiples of π become π, and all even multiples of π become 0; Unknown angle is regarded as positive acute angle in inductive formula.

That is, the first quadrant X, the fourth quadrant -x, the second quadrant π/2+x, the first quadrant π/2-x, the third quadrant π+x, the second quadrant π-x, the fourth quadrant 3π/2+x, the third quadrant 3π/2-x and the fourth quadrant π/2+X..

The laws of sine, cosine, tangent and cotangent symbols in each quadrant are as follows:

One is all positive, two are sine, three are tangent and four are cosine;

When the denominator of π is 2, the name changes: sine becomes cosine, cosine becomes sine, tangent becomes cotangent, and cotangent becomes tangent.

For example, simplify sin( 1 1π/2-x).

① sin (11π/2-x) = sin (π/2-x) (even multiples of 2π are removed).

(2) sin (π/2-x) = cosx。 (π/2-x is in the first quadrant, and both are positive. When the denominator of π is 2, the name changes and sine becomes cosine. )

Finally, I'll give you a new learning method: "Learn more before you get in place, and you can use the Nature Society repeatedly." I wish you progress in your study!