1 multiplication and factorization of all equations in junior high school mathematics;
a2-b2=(a b)(a-b)
a3 b3=(a b)(a2-ab b2)
a3-b3=(a-b)(a2 ab b2)
Trigonometric inequality:
|a b|≤|a| |b|
|a-b|≤|a| |b|
| a |≤b & lt； = & gt-b≤a≤b
|a-b|≥|a|-|b|-|a|≤a≤|a|
All formulas for solving equations in junior high school mathematics 2. Solution of quadratic equation in one variable;
-b √(b2-4ac)/2a-b-b √(b2-4ac)/2a
Relationship between root and coefficient
X1x2 =-b/ax1* x2 = c/a note: Vieta's theorem.
Discriminant b2-4a=0 Note: The equation has two equal real roots.
B2-4ac >0 Note: The equation has real roots.
B2-4ac & lt； 0 Note: The equation has multiple yokes.
A complete set of equations -3 formula method in junior middle school mathematics
First, we should judge how many roots there are in a quadratic equation by the discriminant of the roots of δ = B2-4ac.
1. When δ = B2-4ac
2. When δ = B2-4ac = 0, x has two identical real roots, namely x 1=x2.
3. When δ = B2-4ac >; When 0, x has two different real roots.
When the judgment is completed, if the equation has roots and can belong to two situations, the equation can be based on the formula: x = {-b √ (B2-4ac)}/2a.
In order to find the root of the equation
Formula method is a general method to solve the quadratic equation of one variable, and it is the key to open the key door.
All formulas for solving equations in junior high school mathematics: Daquan 4 two-angle sum formula;
sin(A B)=sinAcosB cosAsinB
sin(A-B)=sinAcosB-sinBcosA
cos(A B)=cosAcosB-sinAsinB
cos(A-B)=cosAcosB sinAsinB
tan(A B)=(tanA tanB)/( 1-tanA tanB)
tan(A-B)=(tanA-tanB)/( 1 tanA tanB)
ctg(A B)=(ctgActgB- 1)/(ctgB ctgA)
ctg(A-B)=(ctgActgB 1)/(ctg b-ctgA)