Sine Theorem/Cosine Theorem ① Sine Theorem: The angle opposite to any side is equal to twice the radius of the circumscribed circle.
② Cosine theorem: the cosine of an angle is equal to the sum of squares of adjacent sides minus the square of the opposite side, and then divided by twice the product of adjacent sides.
It is not recommended to use these two theorems in big questions. You can use them directly when filling in, or you can use the proof of sine theorem to think about ideas.
The head and tail are folded together, for example, 28*22, two digits, ten digits 2 are the same, and the unit digit is 8+2= 10, so it is called head-tail folding.
Clever calculation method:
Mantissa multiplication, the answer is the last two digits; The first time (head+1), from the first time to the second time, you can get the product. For example, 28*22, mantissa multiplication: 2*8= 16, 2*(2+ 1)=6, and the order is 6 16.
The degree of the tangent angle theorem is equal to half of the degree of the central angle of the arc it clips, and equal to the degree of the central angle of the arc it clips.
The above are some theorems suitable for junior high school, and I hope they can help you.