特殊解题方法（Special problem-solving method）.docVIP

特殊解题方法（Special problem-solving method） Collected by oneself Mistakes are unavoidable For reference only In case of error Please correct me! Thank you Special problem-solving method [exhaustive method] answer some mathematical questions A limited number of circumstances or conclusions that may be involved in a problem List all without repetition or omission In order to reach the goal of solving the problem The solution to this problem is exhaustion 1 cases from a to B are A, B, C three routes From the place of propylene are D, E, F, G four routes Ask from a B C to arrive after the total number of routes? (as shown in Figure 3.28) Analysis: there are 3 routes from a to B From B to C area there are 4 routes From a B C to arrive after a total of the following different routes Solution: 3 x 4 = 12 Answer: there are 12 routes Example 2 if an integer With 1, 2, 3 these three numbers Through the operation (add parentheses) add, subtract, multiply and divide to form formula Can make the result equal to 24 Then this integer is called available In the 4, 5, 6, 7, 8, 9, nine, 10, 11, 12 these numbers There is a _______ available (1992 Primary School Mathematical Olympiad Preliminary exam) Analysis: according to the problem A method of column calculation List all the formulas 4 x (1 2 3) (512) = 24 x 3 = 24 6 x (32L) = 247 * 30 ten 2-24 beans 8 x 3 x (2-1) = 249 * 3-1-2-24 10 x 2l3 = 2411 * 23L = 24 12 x (312) = 24 Through calculation, we can see that The 9 numbers given in the question can be made up of 1, 2 and 3, and the result is 24 Answer: there are 9 available numbers 3 cases from 0, 3, 5, 7 selected three numbers can be arranged _______ three digit Which can be three digits divisible by 5 is a _________ (1993 national primary school mathematics contest preliminary examination questions) Analysis: according to the figures given in the question: There are only three choices for a three digit number: The ten digit takes a number in the remaining three digits There are 3 choi