Derivation of the Pythagorean Trigonometric Identities
Pronunciation: /ˌdɛɹ.ɪˈveɪ.ʃən ʌv ðə pɪˌθæ.gəˈri.ən ˌtrɪɡ.ə.nəˈmɛ.trɪk aɪˈdɛn.tə.tiz/ Explain
Derivation of
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A2 + B2 = C2 |
This is the equation given by the Pythagorean Theorem. |
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Use the multiplicative property of equality to multiply both sides by . |
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Since anything except zero divided by itself is one, substitute 1 for . |
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Use the distributive property of multiplication over addition and subtraction to distribute through the parentheses on the left side of the equation. |
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Apply the distributive property of exponentiation over division. |
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The definition of sine is . The definition of cosine is . Given angle θ, and . Apply the substitution property of equality to substitute sin θ for and cos θ for . |
Derivation of
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Start with the first Pythagorean identity. |
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Apply the multiplication property of equality to the equation by multiplying both sides of the equation by . |
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Apply the distributive property of multiplication over addition and subtraction. |
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Since anything except zero divided by itself is one, substitute 1 for . |
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Since 12 = 1, apply the substiution property of equality to subtitute 12 = 1 for 1. |
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Apply the distributive property of exponentiation over division to both sides of the equation. |
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Use the definition of tangent to subsitute tan θ for . |
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Use the definition of secant to subsitute sec θ for . |
Derivation of
Image | Equation | Discussion |
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Start with the first Pythagorean identity. |
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Apply the multiplication property of equality to the equation by multiplying both sides of the equation by . |
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Apply the distributive property of multiplication over addition and subtraction. |
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Since anything except zero divided by itself is one, substitute 1 for . |
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Apply the commutative property of addition. |
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Since 12 = 1, apply the substiution property of equality to subtitute 12 = 1 for 1. |
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Apply the distributive property of exponentiation over division to both sides of the equation. |
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Use the definition of tangent to subsitute cot θ for . |
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Use the definition of secant to subsitute csc θ for . |
References
- McAdams, David E.. All Math Words Dictionary, derivation. 2nd Classroom edition 20150108-4799968. pg 58. Life is a Story Problem LLC. January 8, 2015. Buy the book
Cite this article as:
McAdams, David E. Derivation of the Pythagorean Trigonometric Identities. 12/21/2018. All Math Words Encyclopedia. Life is a Story Problem LLC. https://www.allmathwords.org/en/t/ti_pythagorean.html.
Image Credits
Revision History
12/21/2018: Reviewed and corrected IPA pronunication. (
McAdams, David E.)
7/4/2018: Removed broken links, updated license, implemented new markup, implemented new Geogebra protocol. (
McAdams, David E.)
4/29/2011: Initial version. (
McAdams, David E.)