1, product and difference formula formula formula: sine cosine (=) is positive, cosine sine (=) is negative and cosine cosine cosine (=) is positive, half of the coefficient should be remembered, the relationship between angles changes, and the formula symbol memory method is that cosine is reduced to sine, cosine is added to cosine, synonym is reduced, and the same name is added, and the power is high. Sum product formula formula formula: sine+sine, front sine, sine-sine, back sine, cosine+cosine, cosine side by side, cosine-cosine, cosine aside.

2. In a triangle, the ratio of the sine of each side to its diagonal is equal to the diameter of the circumscribed circle of the triangle. It is known that a triangle is fixed and its solution is unique. It is known that the diagonal of two sides and one side of a triangle is unstable, so its solution is uncertain. We can consider and solve the problem by combining the plane geometry drawing method, the theorem of big side to big angle, the theorem of big angle to big side and the theorem of triangle interior angle.

3. Sine wave is a periodic waveform, and it is the only waveform with a single frequency component. Most periodic waveforms can be converted into a combination of sine waves with different frequencies, amplitudes and phases. The derivative of sine wave is still sine wave, and the integral of sine wave is still sine wave.

Other common mathematical formulas

1, sum formula: ∑(n= 1, n =∞) n =11/2+1/3+...+1/n.

2. quadrature formula: ∏(n= 1, n =∞) n = 1× 2× 3× ...

3. Sine theorem: sin(a)/sin(b)=2R (where r is the radius of the circumscribed circle).

4. Cosine theorem: cosa=(b? +c？ -a？ )/2bc，cosb=(a？ +c？ -B? )/2ac，cosc=(a？ +b？ -c？ )/2ab .

5. Tangent theorem: tana/tanb=2R (where r is the radius of the circumscribed circle).