My Math Forum  

Go Back   My Math Forum > High School Math Forum > Trigonometry

Trigonometry Trigonometry Math Forum

Thanks Tree2Thanks
  • 1 Post By greg1313
  • 1 Post By Country Boy
LinkBack Thread Tools Display Modes
August 5th, 2018, 11:50 PM   #1
Senior Member
Joined: Nov 2015
From: USA

Posts: 101
Thanks: 6

Odd answers on solving triangles

I'm trying to figure out the length of the hypotenuse as the angle grows from 90 to 180 degrees.

However, the results I'm getting say that 180 degrees has a shorter length than 135 degrees, which is wrong.

At 180 degrees, Side + Side = Hypotenuse. (it is just a line, with two short lengths equaling the long length)

I started with side lengths of 3 and 4, but at 135 degrees, the math says the hypotenuse is 6.997, and at 180 degrees it says 6.273.

I can draw it on paper and see how wrong this is.

But as near as I can tell, I'm doing the steps right,

do brackets (googling the cosine)
enter into calculator and get

double checking the calculator

So I'm still getting the wrong answer.

What am I missing?

I know that a triangle with no area (the angle across from the hypotenuse being 180 degrees), with the short sides of 3 and 4 has a hypotenuse of 7.

But I've done this with 135 degrees as well (90 plus 45. Also drawn and measured as shorter than 6.997), and still get an incorrect answer.
Is google wrong on the cosine, or do I need to use something different for angles over 90 degrees like with sine?
MystMage is offline  
August 6th, 2018, 01:00 AM   #2
Global Moderator
greg1313's Avatar
Joined: Oct 2008
From: London, Ontario, Canada - The Forest City

Posts: 7,842
Thanks: 1068

Math Focus: Elementary mathematics and beyond
cos(180$^\circ$) = -1. The calculator you are using is giving results for a radian measure.
Thanks from topsquark
greg1313 is offline  
August 6th, 2018, 01:35 AM   #3
Global Moderator
Joined: Dec 2006

Posts: 19,285
Thanks: 1681

Agreed. Google seems to understand cos(180 deg), so try that instead.
skipjack is offline  
August 6th, 2018, 01:35 AM   #4
Senior Member
Joined: Nov 2015
From: USA

Posts: 101
Thanks: 6

Ah, radians. Thank you.
MystMage is offline  
August 9th, 2018, 01:49 PM   #5
Joined: Jul 2015
From: Jonesborough, TN

Posts: 3
Thanks: 0

It's not a triangle if the length of two sides are not greater than the third side.

Triangle inequality theorem....
roguerob is offline  
August 12th, 2018, 03:06 AM   #6
Math Team
Joined: Jan 2015
From: Alabama

Posts: 3,261
Thanks: 893

Also if a triangle has an angle greater than 90 degrees, it is NOT a right triangle so does NOT have a "hypotenuse". You appear to have an obtuse triangle and are trying to determine the length of the side opposite the obtuse angle.
Thanks from topsquark
Country Boy is offline  

  My Math Forum > High School Math Forum > Trigonometry

answers, odd, solving, triangles

Thread Tools
Display Modes

Similar Threads
Thread Thread Starter Forum Replies Last Post
Solving triangles with the given formation using law of sines and cosines materialartist09 Trigonometry 3 November 12th, 2017 07:23 PM
solving 3D triangles rrosa522 Trigonometry 1 May 1st, 2015 01:26 PM
solving triangles rrosa522 Trigonometry 2 April 27th, 2015 05:53 PM
How Could the Answers be Different? Monox D. I-Fly Elementary Math 4 August 3rd, 2014 08:06 AM
Need help with the answers Cryous Trigonometry 11 May 18th, 2014 09:07 PM

Copyright © 2018 My Math Forum. All rights reserved.