Gauss formula:1+2+3++n = n (n+1)/2 (first term+last term) x number of terms ÷2= and non-negative absolute value /a /≥0, complete square: the inverse of a square ≥0 a is: ax-y. Any book multiplied by 0 must be 0ab=ba (ab)c=a(bc). If one factor is 0, the product is 0. Distribution law: a number multiplied by the sum of two numbers is equal to this number multiplied by these two numbers respectively, and then the products are added: a(b+c)=ab+ac divided by a number is equal to the reciprocal of this number. Note: Zero is not divisible by A ÷b=a× 1/b=a/ B Bonus exchange rate: a+b=b+a Multiplication distribution law: ab=ba generation value: increase = original number × increase percentage = original number+increase. = primitive number+primitive number× growth law = primitive number× (1+growth law) Algebraic addition and subtraction: a+(b+c) =a+b+c a-(b+c)=a-b-c How many triangles are there in a polygon? The number of sides minus 2:(n-2) How many pairs of diagonals does a polygon have? N(n-3)/2 Draw a line segment from a point on the edge with vertices. These N deformations can be divided into: (n- 1. With the line segment of each vertex, N deformations can be cut into: the sum of two angles of N triangles-fillet = 360- flat angle = 180 equals 90, and these two angles are complementary angles, referred to as complementary angles, and the sum of these two angles is equal to 180, so these two angles are called complementary angles, referred to as complementary angles. 2 The internal dislocation angles are equal and the two straight lines are parallel. 3. Complement the lateral internal angle. Two straight lines are parallel and perpendicular to the same straight line. The two lines are parallel to each other: 1. The two lines are parallel and the same angle is equal. 2. The two lines are parallel and the internal angles are equal. The two lines are parallel, so much for the time being. Some have no formulas, only written descriptions. If you listen carefully in class at ordinary times, it is still very easy. Math class is mainly to understand the methods at ordinary times. If you still don't understand, add me QQ: 863669 133 and indicate your purpose.