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question:Let n be an integer larger than 1 and let S be the set of n -element subsets of the set {1,2,ldots,2n} . Determine [max_{Ain S}left (min_{x,yin A, x neq y} [x,y]right )] where [x,y] is the least common multiple of the integers x , y .
answer:1. **Define the Set and Odd Values:** Let ( T = {1, 2, ldots, 2n} ). Define the *odd value* of an element ( t in T ) as the largest odd divisor of ( t ). The odd values are in the set ( U = {1, 3, ldots, 2n-1} ). 2. **Analyze the Set ( A ):** Consider any ( n )-element subset ( A ) of ( T ). Since ( A ) has ( n ) elements and ( U ) has ( n ) elements, the odd values of two elements in ( A ) must either be the same or the set of all odd values of the elements of ( A ) must be ( U ). 3. **Case 1: Two Elements with the Same Odd Value:** Suppose there are two elements in ( A ) with the same odd value. Let these elements be ( 2^a c ) and ( 2^b c ) where ( c in U ). Then, [ [2^a c, 2^b c] = 2^{max(a, b)} c leq 2n. ] Thus, the minimum value of the least common multiple (LCM) of two elements in ( A ) is at most ( 2n ). 4. **Case 2: All Odd Values are Distinct:** Suppose the odd values of ( A ) form the whole set ( U ). For any two elements of ( A ) with different odd values, replacing ( u ) by ( 2u ) (if ( u leq n )) will not decrease the minimum LCM and is valid since ( 2u leq 2n ). Thus, the set ( A ) for which the minimum LCM is maximized is ( {n+1, n+2, ldots, 2n} ). 5. **Representing Elements of ( A ):** The elements of ( A ) can be represented as ( {1 cdot 2^{b_1}, 3 cdot 2^{b_3}, ldots, (2n-1) cdot 2^{b_{2n-1}}} ) where ( b_i ) are nonnegative integers. If ( i < j ) are odd integers, then ( b_i geq b_j ) because if ( b_i < b_j ), [ i cdot 2^{b_i + 1} leq i cdot 2^{b_j} < j cdot 2^{b_j} leq 2n, ] which is a contradiction. 6. **Calculating the LCM:** Suppose ( i < j ) are odd integers such that ( i mid j ). Since ( i mid j ) and both are odd, ( j geq 3i ). Therefore, [ [2^{b_i} cdot i, 2^{b_j} cdot j] = 2^{max(b_i, b_j)} cdot [i, j] = 2^{b_i} cdot j geq 2^{b_i} cdot 3i = 3 cdot (2^{b_i} cdot i). ] If ( i notmid j ), there exists an odd prime ( p ) that divides ( i ) more times than it divides ( j ). Therefore, [ [i, j] geq pj geq 3j. ] Thus, [ [2^{b_i} cdot i, 2^{b_j} cdot j] geq 2^{b_i} cdot 3j = 3 cdot (2^{b_i} cdot j). ] The LCM of any two elements of ( A ) is at least ( 3 cdot (i cdot 2^{b_i}) ) where ( i cdot 2^{b_i} in A ), which is at least ( 3(n+1) ). 7. **Special Cases:** - If ( n = 2 ), ( A = {3, 4} ), the desired value is ( 12 ). - If ( n = 4 ), ( A = {5, 6, 7, 8} ), the desired value is ( 24 ). 8. **General Case for Even ( n geq 6 ):** Let ( n ) be an even integer. Note that ( n+2 ) is even. Let ( u ) be the odd part of ( n+2 ). Since ( u leq (n+2)/2 leq 2n/3 ), ( 3u leq 2n ). Thus, ( 3(n+2) ) is an achievable LCM. To show this is the least possible value, consider ( [n+1, i] > 3(n+2) ) for all ( n+1 < i leq 2n ). Let ( v ) be the odd part of ( i ). If ( v leq n ), then ( b_v geq 1 ), implying [ [n+1, i] geq 3(n+1) cdot 2^{b_v} geq 6(n+1) geq 3(n+2). ] If ( v > n ), then ( i = v > n+1 ), implying [ [n+1, i] geq 3 cdot 2^{b_i} cdot i geq 3(n+2). ] Therefore, if ( n ) is even, ( 3(n+2) ) is the desired value. The final answer is ( boxed{3(n+1)} ) if ( n ) is odd, ( boxed{3(n+2)} ) if ( n geq 6 ) is even, ( boxed{12} ) if ( n = 2 ), and ( boxed{24} ) if ( n = 4 ).
question:Given the question: I am trying to decide whether it's worth it to invest in this film proposal. Can you help me answer a few questions? If you can't, please say No I can't. Question: What has the footage of Charles drowning in his pool? Movie title: April Fool's Day Movie plot: On April 1, 2007, Desiree Cartier is hosting a party at her mansion for her actress friend Torrance Caldwell. Present for a pre-festivities toast areâBlaine Cartier, Desiree's brother, who controls their joint inheritance (to Desiree's dislike), U.S. Senate candidate Peter Welling, Peter's Miss Carolina fiancee Barbie Reynolds, and the quintet's less wealthy videographer friend Ryan. With the party in full swing, Desiree's social nemesis and Ryan's not-so-secret crush Milan Hastings, arrives. Also present is chihuahua-toting society reporter Charles. As another in her long string of April Fool's pranks, Desiree suggests Blaine get Milan tipsy on champagne and seduce her in his bedroom upstairs. Desiree and several of the others hover by the cracked-open bedroom door, prepared to videotape the affair with the camera Desiree lifted from Ryan. However, Milan has a seizure and falls off the balcony to her death. The group goes to court, and Blaine loses control of the family's fortune, which shifts to Desiree, but they are considered innocent and Milan's death is considered a fatal prank. One year later, Desiree, Blaine, Peter, Barbie, Torrance, and Ryan receive anonymous invitations to meet on Milan's grave at noon, April 1, 2008, with the cryptic P.S. I have proof. Just after the entire sextet is back together, a messenger comes to the grave with a box containing a letter and a laptop computer. The letter says one of the six murdered Milan, and if that person does not confess, all of them will be dead by midnight. As a show of intent, the computer has footage of Charles drowning in his pool. Everyone goes from the cemetery to the pool to confirm this mishap. Subsequently, an increasingly frantic Desiree sees one suspect after another murdered before her eyes (though the bodies keep disappearing). Barbie is electrocuted in a beauty pageant dressing room, Peter's campaign truck runs him down in a parking garage, Ryan's throat is slit in his humble apartment, and returning home, Desiree and Blaine... The answer is:
answer:The footage of Charles drowning in his pool serves as evidence and a show of intent by the anonymous threat-maker. The letter sent to Desiree, Blaine, Peter, Barbie, Torrance, and Ryan claims that one of the six people murdered Milan, and if that person does not confess, all of them will be dead by midnight. The footage of Charles drowning is included on the laptop computer as a warning to the group, demonstrating that the threat is serious and not just another April Fool's prank. The party attendees, who all played a role in Milan's fatal prank a year before, receive anonymous invitations to gather at Milan's grave. It's there that a messenger delivers a box containing the letter and laptop computer. Once the group confirms Charles' death by visiting his pool, they are all in fear of their lives, especially Desiree, as she begins to witness her friends being murdered one by one. This creates a sense of urgency for the group to figure out who is responsible and confess in order to avoid the promised deaths by midnight. In conclusion, the footage of Charles drowning in his pool provides evidence of the anonymous threat-maker's deadly intentions, creating suspense and tension in the movie as the characters scramble to uncover their blackmailer's identity and avoid meeting a similar fate themselves.
question:Solve for x in 6x^3 - 5x^2 - 12x + 4 = 0 given that x = 2/3 is a solution to the equation.
answer:We are given a cubic equation 6x^3 - 5x^2 - 12x + 4 = 0, and we know that x = 2/3 is one of its solutions. This means that (3x - 2) is a factor of the polynomial. To solve for x, we can perform polynomial division to factor the equation. Dividing 6x^3 - 5x^2 - 12x + 4 by (3x - 2), we get 2x^2 - x - 2 as the quotient. So, the original equation can be factored as (3x - 2)(2x^2 - x - 2) = 0. Now we have two equations set equal to zero: 3x - 2 = 0, which we already know has a solution at x = 2/3, and the quadratic equation 2x^2 - x - 2 = 0. To solve the quadratic equation, we can use the quadratic formula: x = (-b ± √(b^2 - 4ac)) / 2a. For the equation 2x^2 - x - 2 = 0, a = 2, b = -1, and c = -2. Plugging these values into the formula, we get x = (1 ± √((-1)^2 - 4(2)(-2))) / (2(2)), which simplifies to x = (1 ± √(1 + 16)) / 4, or x = (1 ± √17) / 4. Therefore, the solutions to the given equation are x = 2/3 and x = (1 ± √17) / 4.
question:What is an imaginary unit?
answer:The imaginary unit, denoted by i, is a fundamental concept in mathematics that extends the real number system to the complex number system. It is defined as the square root of -1, denoted by i = √(-1). In other words, i is a number that satisfies the equation i^2 = -1. The term imaginary might be misleading, as it suggests that i is not a real number in the classical sense. However, i is a well-defined mathematical object that plays a crucial role in many areas of mathematics, physics, and engineering. The introduction of i allows us to extend the real number system to the complex number system, which consists of numbers of the form a + bi, where a and b are real numbers and i is the imaginary unit. This extension enables us to solve equations that cannot be solved using only real numbers, such as x^2 + 1 = 0, which has solutions x = ±i. Geometrically, complex numbers can be represented as points in a two-dimensional plane, known as the complex plane, where the x-axis represents the real part and the y-axis represents the imaginary part. The imaginary unit i can be thought of as a 90-degree rotation in the complex plane, which is a fundamental concept in many mathematical and physical applications. The concept of the imaginary unit has far-reaching implications in many areas of mathematics, including algebra, calculus, differential equations, and number theory, as well as in physics, electrical engineering, and other fields.