| author | wenzelm |
| Sat, 23 May 2015 17:19:37 +0200 | |
| changeset 60299 | 5ae2a2e74c93 |
| parent 59190 | 3a594fd13ca4 |
| child 61343 | 5b5656a63bd6 |
| permissions | -rw-r--r-- |
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(* Title: HOL/ex/Pythagoras.thy |
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Author: Amine Chaieb |
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*) |
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header "The Pythagorean Theorem" |
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theory Pythagoras |
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imports Complex_Main |
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begin |
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text {* Expressed in real numbers: *}
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lemma pythagoras_verbose: |
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"((A1::real) - B1) * (C1 - B1) + (A2 - B2) * (C2 - B2) = 0 \<Longrightarrow> |
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(C1 - A1) * (C1 - A1) + (C2 - A2) * (C2 - A2) = |
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((B1 - A1) * (B1 - A1) + (B2 - A2) * (B2 - A2)) + (C1 - B1) * (C1 - B1) + (C2 - B2) * (C2 - B2)" |
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by algebra |
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text {* Expressed in vectors: *}
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type_synonym point = "real \<times> real" |
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lemma pythagoras: |
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defines ort:"orthogonal \<equiv> (\<lambda>(A::point) B. fst A * fst B + snd A * snd B = 0)" |
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and vc:"vector \<equiv> (\<lambda>(A::point) B. (fst A - fst B, snd A - snd B))" |
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and vcn:"vecsqnorm \<equiv> (\<lambda>A::point. fst A ^ 2 + snd A ^2)" |
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assumes o: "orthogonal (vector A B) (vector C B)" |
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shows "vecsqnorm(vector C A) = vecsqnorm(vector B A) + vecsqnorm(vector C B)" |
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using o unfolding ort vc vcn by (algebra add: fst_conv snd_conv) |
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end |