求三个数的最大公约数、最小公倍数,与求两个数的最大公约数、最小公倍数相比,情况比较复杂,难度较大。求三个数的最小公倍数与最大公约数,方法又有区别。这部分内容是“数的整除”教学的难点之一。下面两点应引导学生切实掌握。第一,正确确定短除法的除数与判断最后的商。求三个数的最大公约数,一般先用短除法,每次除必须用三个数的公约数(1除外)作除数,除到三个数只有公约数1为止。而求三个数的最小公倍数,若三个数有公约数(1除外),则用三个数的公约数作除数,若除到三个数只有公约数1,而其中两个数有公约数时(1除外),还要用两个数的公约数(1除外)继续除,一直除到所得的商每两个数都是互质数(即“两两互 Find the greatest common divisor of the three numbers, the least common multiple, compared with the greatest common divisor of the two numbers, the least common multiple, the situation is more complicated and more difficult. Seeking the least common multiple of the three numbers and the greatest common divisor, the method is different again. This part is one of the difficulties in the teaching of divisibility of numbers. The following two points should guide students to effectively grasp. First, the correct determination of the division of the short division and determine the final quotient. Find the greatest common divisor of the three numbers, generally first with the short division method, except that you must divide the common divisor (except 1) by three numbers into the divisor until each of the three numbers has only the common divisor 1. And find the least common multiple of three numbers, if the three numbers have a common divisor (except 1), divide the divisor by the common divisor of the three numbers, if there are only divisor divisor 1 to three, and two of them have conventions (Except 1), but also use the common divisor of two numbers (except 1) to continue dividing until the quotient of every two numbers is a prime number (that is,