Acute trigonometric function: definition of acute trigonometric function: sine (sin), cosine (cos) and tangent (tan), cotangent (cot), secant (sec) and cotangent (csc) of acute angle A are all called acute trigonometric function of angle A.

Sine: the opposite side is more inclined than the hypotenuse, that is, Sina = a/c; Cosine (cos): the adjacent side is more inclined, that is, COSA = b/c; Tangent (tan): the opposite side is greater than the adjacent side, that is, tana = a/b; Cotangent (cot): adjacent edges compare edges, that is, COTA = b/a; Sec: the hypotenuse is closer to the adjacent side, that is, seca = c/b; Cotangent (csc): the comparison between the hypotenuse and the edge, that is, CSCA = C/A.

Trigonometric function memory formula: Trigonometric function is a function, and quadrant symbols are marked. Function image unit circle, periodic parity increase and decrease. The same angle relation is very important, and both simplification and proof are needed. At the vertex of the regular hexagon, cut the chord from top to bottom; Write the number 1 in the middle. A triangle connecting vertices; The sum of squares of a downward triangle, the reciprocal relationship is diagonal, and any function of the vertex is equal to the division of the latter two.

The inductive formula is good. After the negative is positive, it becomes bigger and smaller, and it becomes a tax angle, which is convenient for table lookup and essential for simplification. Semi-integer multiple of two, the odd parity is unchanged, the latter is regarded as an acute angle, and the symbol is judged by the original function. The cosine value of the sum of two angles is converted into a single angle for easy evaluation, and the sine product is subtracted from the cosine product, which distorts the variable angle formula. Sum and difference products must have the same name, and the complementary angle must be renamed.