First, see the problem of "evaluation angle" and apply the "emerging" inductive formula? One-step conversion to the formula of interval (-90o, 90o).

1 . sin(kπ+α)=(- 1)ksinα(k∈Z).

2.cos(kπ+α)=(- 1)kcosα(k∈Z).

3.tan(kπ+α)=(- 1)ktanα(k∈Z).

4.cot(kπ+α)=(- 1)kcotα(k∈Z).

Click to view: high school mathematics trigonometric function inverse formula summary.

Second, look at the problem of "sin α cos α" and use the triangle "gossip".

1 . sinα+cosα& gt； 0 (or

2.sinα-cosα& gt； 0 (or

3. The terminal edges of | sin α | > | cos α | α are in regions II and III.

4. The terminal edges of | sin α | <| cos α | ó α are in zone I and zone IV.

Third, look at the problem of "known 1 finding 5", do Rt△, and memorize the commonly used pythagorean numbers (3, 4, 5), (5, 12, 13), (7, 24, 25) by using pythagorean theorem.

Fourth, the problem of "cutting" is transformed into the problem of "string".

Verb (abbreviation of verb) "See Qi Sixian" = > "Change the chord into one": Given tanα, find the homogeneous formula of sinα and cosα. In some algebraic expressions, the denominator can be regarded as 1, which can be converted into sin2α+cos2α.

For intransitive verbs, refer to the "Square Difference of Sine or Angle" table, and enable the "Square Difference" formula:

1 . sin(α+β)sin(α-β)= sin 2α-sin 2β.

2.cos(α+β)cos(α-β)= cos2α-sin2β.

Seven, look at the problem of "sin α cosα and sinαcosα", and apply the square law:

(sinα cos α) 2 =12sinα cos α =1sin2alpha, so:

1. If sinα+cosα=t (and t2≤2), then 2sinαcosα=t2- 1=sin2α.

2. If sinα-cosα=t, (and t2≤2), then 2sinαcosα= 1-t2=sin2α.