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Pigeonhole principle and inclusion, exclusion
Two counting ideas that prove things without listing anything.
Pigeonhole: more pigeons than holes means some hole holds two. Inclusion, exclusion: |A ∪ B| = |A| + |B| − |A ∩ B|, and the alternating sum continues for more sets. Picture it: a Venn diagram; the overlap is what you counted twice. Think it: inclusion, exclusion is the Möbius function of the subset lattice.
हल किया गया उदाहरण · {1,2,3,4} union {3,4,5,6}
{1,2,3,4} union {3,4,5,6}
चरण दर चरण
- A = \left\{1, 2, 3, 4\right\},\quad B = \left\{3, 4, 5, 6\right\}
The two sets.
- A \cup B = \left\{1, 2, 3, 4, 5, 6\right\}
Keep everything in either set.
- |A| = 4,\ |B| = 4,\ |A \cup B| = 6
Cardinalities. Note |A ∪ B| = |A| + |B| − |A ∩ B|.
जवाब दिखाएँ
अब आप कोई प्रश्न चुनें, या अपना प्रश्न टाइप करें या बनाएं। हर चरण, एक चित्र, और उत्तर तब तक छिपा रहता है जब तक आप न पूछें।
एक स्वतंत्र वृत्तान्त प्रत्येक पाठ पर आगे कहता है, जो आपने पूरा किया है, आपके हल किये गये समस्याओं का रिकॉर्ड, और एक शिक्षक जिसके बारे में आप पूछ सकते हैं ।
साइन अप करें लॉगिनयहाँ उपयोग में संकेत
पूरी परिभाषा, चित्र, और इसमें हर अक्षर का अर्थ क्या है?
कैसे: Pigeonhole principle and inclusion, exclusion
- The two sets.
- Keep everything in either set.
- Cardinalities. Note |A ∪ B| = |A| + |B| − |A ∩ B|.
लोग जो सवाल पूछते हैं
Permutation or combination?
Ask whether order matters. A lock code is a permutation (order matters); a hand of cards is a combination (it does not).
What is a graph in this sense?
Dots (vertices) joined by lines (edges), not a plot. Road maps, social networks and molecules are graphs; questions like "is there a route" and "how few colours" are graph theory.
More in Combinatorics & Graph Theory
The counting principlesBinomial coefficients and Pascal's triangleRecurrences and generating functionsGraphs: vertices, edges, degreesPaths, cycles, trees, Euler and HamiltonColouring and planar graphs