The general formula (a, b, c are real numbers, and a≠0) matches the formula A (X+B/2A) 2 = (B 2-4ac)/4a. Two formulas a(x-x 1)(x-x2)=0. The formula X = (-B+). And "formula method" (divided into "square difference formula" and "complete square formula"), as well as "cross multiplication". The factorization method is obtained by factorizing the left side of the equation, and the content of factorization was learned in the last semester of Grade 8. For example, 1. Solve the equation: x 2+2x+ 1 = 0. Solve by the factor of the complete square formula: (x+ 1). 2 = 0 solution: x 1= x2=- 1 2. Solution of equation x(x+ 1)-2(x+ 1)=0: By increasing the common factor, we get: (X-2) (X+65433). X2=- 1 3。 Solution of equation x2-4=0 Solution: (x+2)(x-2)=0 x+2=0 or x-2=0 ∴ x 1=-2, X2= 2 Cross multiplication formula: x2+(p+q) x+pq = (x+). AB+2B+A-B-2 = AB+A 2-B-2 = A (B+65433) formula method (which can solve all the quadratic equations of one variable) To find the root formula, we must first judge how many quadratic equations of one variable have through the discriminant of the roots of δ = b 2-4ac. When δ = b 2-4ac0, X has two different real roots. When the judgment is completed, if the equation has roots, it can belong to two situations: 2 and 3. If the equation has roots, we can find the root collocation method of the equation according to the formula: x = {-b √ (b 2-4ac)}/ 2a (all quadratic equations in one variable can be solved), such as: solving the equation: x 2+2x-3 = 0 solution: moving the constant term to: x 2+2x = 3, And add 1 to both sides of the equation at the same time (to form a completely flat way) to give: x 2+2x+ 1 = X2= 1 collocation method formula: change the quadratic coefficient into a constant and move it to the right once. Add the most equivalent open method (which can solve the partial quadratic equation) on both sides, such as: x 2-24 = 1 solution: x 2 = 25 x = 5 ∴ x 65438+ for example: x 2-70x+825 m=20, the average value is 35, and let x1= The relationship between roots and coefficients of a quadratic equation with one variable (the following two formulas are very important and often used in exams) (Vieta theorem) General formula: the relationship between two roots of a 2+bx+c = 0x1and x2: x1+x2 =-b/ax1x2 = c.