1, square root calculation formula: the number in the root sign can be changed to the same or the same, so it can be added and subtracted, but not different. If the numbers in the root sign are the same, they can be added or subtracted; If the numbers in the root sign are different, you can't add or subtract; If you can simplify it to numbers with the same root sign, you can add and subtract.
The multiplication and division of the radical sign: √ a/b = √ a √ b √ a ≥ 0b ≥ 0 √ and √ a/b = √ a √ b.
2. Formulas that must be remembered in solving equations
Multiplication and factorization: A2-B2 = (A+B) (A-B); a3+B3 =(a+b)(a2-a b+B2)； a3-b3=(a-b)(a2+ab+b2).
The solution of the unary quadratic equation:-b+√ (B2-4ac)/2a-b-b+√ (B2-4ac)/2a.
Trigonometric inequality: | a+b |≤| a |+b |; | a-b |≤| a |+| b |； | a |≤b & lt； = & gt-b≤a≤b； |a-b|≥|a|-|b|-|a|≤a≤|a| .
Key knowledge points of junior high school mathematics
Parallelism: ① Two straight lines that do not intersect in the same plane are called parallel lines. ② One and only one straight line is parallel to this straight line after passing through a point outside the straight line. If both lines are parallel to the third line, then the two lines are parallel to each other.
Perpendicular: ① If two lines intersect at right angles, they are perpendicular to each other. (2) The intersection of two mutually perpendicular straight lines is called vertical foot. ③ On the plane, there is one and only one straight line perpendicular to the known straight line at one point.
Perpendicular bisector: A straight line perpendicular to and bisecting a line segment is called perpendicular bisector.
The perpendicular bisector in perpendicular bisector must be a line segment, not a ray or a straight line, which is related to the infinite extension of rays and straight lines. Look at the back, the middle vertical line is a straight line, so when drawing the middle vertical line, be sure to draw two points after the line segment passes through two points (about painting, we will talk about it later).