Mathematical wide angle refers to using some simple mathematical knowledge to combine and get new results. In junior high school, we often use the wide-angle collocation of mathematics. The following is a brief introduction to how to use these skills:

1, replace the equation with algebraic expression.

(1) Convert an equation into two or three equations (such as 3x+2y= 1 1), and then determine which one is the root as needed; If these two or three equations are roots, they can be regarded as a solution of the original equation.

(2) Multiply the left and right sides of an equation by the same number (such as 4X+Y= 15), and then decide which side is the root as needed. (Note: 4X and y in 4X+Y= 15 must be equal)

(3) Use the product of one inequality and another inequality to determine the root of the original inequality. (Note: When 3x-2y=3, 3x-3y=2. )

(4) Use two algebraic expressions to represent the product of two numbers, and then use the value of one algebraic expression to determine the criterion of the root of the other.

2. Use special values

(1) When the absolute value of a number is greater than or equal to a certain value, (for example, 2 5 >; =5), then it is the negative multiple of the maximum value of the absolute value of this value; On the contrary, push backwards. 3x-4y & lt； At 1, 4xy

(2) For some numbers, (for example, 6 * 7 >; =6*8 or 9 *10 > =9* 1 1), then its minimum value is 6*7 and its maximum value is 9 *10; Or push it back. 3x-7z & lt； 0，7zy≤3。