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用短除法求三个数的最小公倍数,教学上有两个难点。第一是计算过程复杂,要先用这三个数的公约数去除;再用其中两个数的公约数去除,把另一个数移下来,这一点学生很难理解。例如求12、16、18的最小公倍数,可从观察质因数入手,学生较易接受。①先用列举法找出它们的最小公倍数,并把它分解质因数。144=2×2×3×2×2×3 ②把12、16、18分别分解质因数。12=2×2 ×3 16=2×2×2×2 18=2 ×3×3 ③通过观察,学生发现:144的全部质因数为2、2、3、2、2、3与三个数的质因数相比较,
Find the least common multiple of the three numbers by the short division method, which has two difficulties in teaching. The first is that the computational process is complicated. It is necessary to first remove the common divisors of the three numbers, remove them by the common divisor of two of them, and make it hard for students to understand. For example, find the least common multiple of 12,16,18, starting from the observation of prime factors, students are more acceptable. First use the enumeration method to find out their least common multiple, and its decomposition factor. 144 = 2 × 2 × 3 × 2 × 2 × 3 ② The factorization of 12,16,18, respectively. 12 = 2 × 2 × 3 16 = 2 × 2 × 2 × 2 18 = 2 × 3 × 3 Through the observation, the student found that: 144 all the prime factors of 2,2,3,2,2,3 and three The number of primes compared,