1, algebraic formula and rational formula: the formula formed by connecting numbers or letters representing numbers with operation symbols is called algebraic formula. A single number or letter is also algebraic. Algebraic expressions and fractions are collectively called rational forms.

2. similar triangles's judgment: A straight line parallel to one side of a triangle intersects with other two sides or extension lines of both sides, and the triangle formed is similar to the original triangle.

3. Distinguish algebraic expressions from fractions according to whether there are letters in the division formula; According to whether there are addition and subtraction operations in algebraic expressions, monomial and polynomial can be distinguished.

4. After being converted into the simplest quadratic root, quadratic roots with the same number of roots are called similar quadratic roots.

5. Diagonal: Two sides of one angle are relative extension lines of another angle, and two angles like this are diagonal to each other.