Uploaded April 2023 | Updated September 2026, 1 week ago
Learn more about the law of sine and cosine on Brilliant: brilliant.org/blackpenredpen (now with a 30-day free trial)
I came up with this tricky test question challenge for my precalculus students. Start with an obtuse triangle, give students the length of all three sides and one of the acute angles. Ask the students to find the measure of the obtuse angle. Now many students will proceed by using the Law of Sine because the formula is shorter compared to the Law of Cosine. But because the range of the inverse sine function is _________, we will have to be extra careful with we use the Law of Sine!
Written solutions for this problem: patreon.com/posts/81996867
My trig worksheets (for everyone): patreon.com/posts/81996734
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๐ช Support this channel and get my math notes by becoming a patron: patreon.com/blackpenredpen
๐ Shop my math t-shirt & hoodies: amzn.to/3qBeuw6
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๐ช Support the channel and get featured in the video description by becoming a patron: patreon.com/blackpenredpen
AP-IP Ben Delo Marcelo Silva Ehud Ezra 3blue1brown Joseph DeStefano
Mark Mann Philippe Zivan Sussholz AlkanKondo89 Adam Quentin Colley
Gary Tugan Stephen Stofka Alex Dodge Gary Huntress Alison Hansel
Delton Ding Klemens Christopher Ursich buda Vincent Poirier Toma Kolev
Tibees Bob Maxell A.B.C Cristian Navarro Jan Bormans Galios Theorist
Robert Sundling Stuart Wurtman Nick S William O'Corrigan Ron Jensen
Patapom Daniel Kahn Lea Denise James Steven Ridgway Jason Bucata
Mirko Schultz xeioex Jean-Manuel Izaret Jason Clement robert huff
Julian Moik Hiu Fung Lam Ronald Bryant Jan ลehรกk Robert Toltowicz
Angel Marchev, Jr. Antonio Luiz Brandao SquadriWilliam Laderer Natasha Caron Yevonnael Andrew Angel Marchev Sam Padilla ScienceBro Ryan Bingham
Papa Fassi Hoang Nguyen Arun Iyengar Michael Miller Sandun Panthangi
Skorj Olafsen Riley Faison Rolf Waefler Andrew Jack Ingham P Dwag Jason Kevin Davis Franco Tejero Klasseh Khornate Richard Payne Witek Mozga Brandon Smith Jan Lukas Kiermeyer Ralph Sato Kischel Nair Carsten Milkau Keith Kevelson Christoph Hipp Witness Forest Roberts Abd-alijaleel Laraki Anthony Bruent-Bessette Samuel Gronwold Tyler Bennett christopher careta Troy R Katy Lap C Niltiac, Stealer of Souls Jon Daivd R meh Tom Noa Overloop Jude Khine R3factor. Jasmine Soni L wan na Marcelo Silva Samuel N Anthony Rogers Mark Madsen Robert Da Costa Nathan Kean Timothy Raymond Gregory Henzie Lauren Danielle Nadia Rahman Evangline McDonald Yuval Blatt Zahra Parhoun Hassan Alashoor Kaakaopuupod bbaa Joash Hall
----------------------------------------
Thank you all!
0:00 my favorite precalculus test question
5:02 a small mistake. c should be 5.8
8:24 Check out Brilliant
Learn more about the law of sine and cosine on Brilliant: brilliant.org/blackpenredpen (now with a 30-day free trial)
I came up with this tricky test question challenge for my precalculus students. Start with an obtuse triangle, give students the length of all three sides and one of the acute angles. Ask the students to find the measure of the obtuse angle. Now many students will proceed by using the Law of Sine because the formula is shorter compared to the Law of Cosine. But because the range of the inverse sine function is _________, we will have to be extra careful with we use the Law of Sine!
Written solutions for this problem: patreon.com/posts/81996867
My trig worksheets (for everyone): patreon.com/posts/81996734
----------------------------------------
๐ช Support this channel and get my math notes by becoming a patron: patreon.com/blackpenredpen
๐ Shop my math t-shirt & hoodies: amzn.to/3qBeuw6
----------------------------------------
๐ช Support the channel and get featured in the video description by becoming a patron: patreon.com/blackpenredpen
AP-IP Ben Delo Marcelo Silva Ehud Ezra 3blue1brown Joseph DeStefano
Mark Mann Philippe Zivan Sussholz AlkanKondo89 Adam Quentin Colley
Gary Tugan Stephen Stofka Alex Dodge Gary Huntress Alison Hansel
Delton Ding Klemens Christopher Ursich buda Vincent Poirier Toma Kolev
Tibees Bob Maxell A.B.C Cristian Navarro Jan Bormans Galios Theorist
Robert Sundling Stuart Wurtman Nick S William O'Corrigan Ron Jensen
Patapom Daniel Kahn Lea Denise James Steven Ridgway Jason Bucata
Mirko Schultz xeioex Jean-Manuel Izaret Jason Clement robert huff
Julian Moik Hiu Fung Lam Ronald Bryant Jan ลehรกk Robert Toltowicz
Angel Marchev, Jr. Antonio Luiz Brandao SquadriWilliam Laderer Natasha Caron Yevonnael Andrew Angel Marchev Sam Padilla ScienceBro Ryan Bingham
Papa Fassi Hoang Nguyen Arun Iyengar Michael Miller Sandun Panthangi
Skorj Olafsen Riley Faison Rolf Waefler Andrew Jack Ingham P Dwag Jason Kevin Davis Franco Tejero Klasseh Khornate Richard Payne Witek Mozga Brandon Smith Jan Lukas Kiermeyer Ralph Sato Kischel Nair Carsten Milkau Keith Kevelson Christoph Hipp Witness Forest Roberts Abd-alijaleel Laraki Anthony Bruent-Bessette Samuel Gronwold Tyler Bennett christopher careta Troy R Katy Lap C Niltiac, Stealer of Souls Jon Daivd R meh Tom Noa Overloop Jude Khine R3factor. Jasmine Soni L wan na Marcelo Silva Samuel N Anthony Rogers Mark Madsen Robert Da Costa Nathan Kean Timothy Raymond Gregory Henzie Lauren Danielle Nadia Rahman Evangline McDonald Yuval Blatt Zahra Parhoun Hassan Alashoor Kaakaopuupod bbaa Joash Hall
----------------------------------------
Thank you all!
0:00 my favorite precalculus test question
5:02 a small mistake. c should be 5.8
8:24 Check out Brilliant
