1, directly given: sometimes, a fixed value is directly given in the problem, such as the side length and angle of a geometric figure.

2. Proportional relationship: If there is a proportional relationship between two quantities, then their ratio is a fixed value. For example, if the corresponding sides of two triangles are proportional, their area ratio will also be a constant value.

3. Algebraic method: through algebraic method, the variables in the problem are expressed as the combination of constants and other variables, so as to find the fixed value. For example, if there is only one unknown in an equation, then this unknown is a fixed value.

4. Using the properties of the equation: the equation is still valid when both sides of the equation add, subtract, multiply and divide the same number at the same time. Using this property, you can get a fixed value.

5. Solving the equation: By solving the equation, the value of the unknown quantity can be obtained, and thus the fixed value can be obtained.

6. Using geometric properties: In geometric problems, some geometric properties can help to find a fixed value, such as the sum of the internal angles of a triangle is 180 degrees, and the degree of the circumferential angle is equal to half the degree of an arc.

7. Using symmetry: If a graph has symmetry, then some of its properties are equal at the symmetry point, and these equal properties can be used to find a fixed value.

8. Using proportional line segments: In geometric problems, if two line segments are proportional, then their length ratio is a constant value.

9. Use similar triangles: If two triangles are similar, their corresponding sides are proportional and their corresponding angles are equal. These proportional and equal relations can be used to find a fixed value.

10. Using Pythagorean Theorem: In a right triangle, the sum of the squares of two right-angled sides is equal to the square of the hypotenuse. This theorem can be used to find the length of the hypotenuse, thus obtaining a fixed value.

1 1. Use the properties of parallel lines: if two lines are parallel, their congruence angles are equal, their internal angles are equal, and their internal angles are complementary. These properties can be used to find the fixed value of angle.

12. Use the properties of the bisector of an angle: If a ray divides an angle into two equal angles, then this ray is called the bisector of this angle, and the two angles divided by the bisector of the angle are equal. This property can be used to find a fixed value of the angle.