Math Problem Statement
Proof by direct proof. Proposition: if a, b,c is an element of natural numbers, then lcm (ca, cb) = c × lcm (a,b) Let m= lcm(ca, cb) and n= c×. Lcm(a, b)
Solution
Proposition:
If , , and are elements of natural numbers, then: Where denotes the least common multiple of and .
We want to prove this using direct proof. Let:
Proof:
Step 1: Express and
- , by definition of the least common multiple, means is the smallest positive integer such that both and divide .
- , where is the least common multiple of and , and multiplying it by scales it accordingly.
We need to show that , i.e., .
Step 2: Factorization of , , and
To better understand the relationship between , , and their least common multiple, we can express , , and in terms of their prime factorizations:
- Let
- Let
- Let , where the prime factors are shared or different.
The least common multiple of two numbers takes the highest power of each prime factor from either number. Thus, the least common multiple of and is:
Multiplying both and by gives:
Step 3: LCM of and
The least common multiple of and is: This simplifies to: This shows that the least common multiple of and is the same as multiplying by the least common multiple of and , which is: Thus, we have:
Conclusion:
We have shown that the least common multiple of and is equal to times the least common multiple of and . Hence, the proposition is proven:
Would you like more details or clarification on any step?
Related Questions:
- What is the definition of the least common multiple (LCM)?
- How do you compute the LCM of two numbers using prime factorizations?
- What properties of the LCM are used in direct proofs?
- Can you extend this proof to three numbers, i.e., ?
- How does the greatest common divisor (GCD) relate to the LCM?
Tip: When dealing with LCM, always consider the prime factorizations of the numbers involved, as LCM is based on the highest powers of common prime factors.
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Math Problem Analysis
Mathematical Concepts
Number Theory
Least Common Multiple (LCM)
Prime Factorization
Formulas
lcm(ca, cb) = c × lcm(a, b)
lcm(a, b) = p_1^max(e_1, f_1) × p_2^max(e_2, f_2) × ... × p_k^max(e_k, f_k)
Theorems
Least Common Multiple (LCM) Theorem
Prime Factorization Theorem
Suitable Grade Level
Grades 10-12
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