HarvardBound1123

Guys you know that question which said there was an isosceles triangle with sides 5,10,10 and asked you to calculate the largest angle?

For that most people con CC say the answer was 29 something...but im fairly confident im right...

c^2 = a^2 + b^2 - 2abcosine(C)

5^2 = 10^2 + 10^2 - 2(10)(10)cosine(c)
25 - 200 = -2(100)cos(c)
-175/-200 = cos(c)
cos(c) = .875
Do inverse cos(.875) you get = 28.955 deg. which is...the SMALLEST angle. so
180 - 28.955 = 151.044
since its isosceles, divide this angle by 2 to get the largest angle
151.0444/2 = 75.522 degress. Which was an answer i belive. thats what i put. im pretty sure this is right.

and if the answer was ~29 or w/e it would have to be the largest angle, therefore since it is isoseceles 29 x 2 = 58 [[sum of two angles is 58]] 180 - 58 = 122. clearly a larger angle. so how can ~29 deg. be right?

elaslawek

It wasnt asking for the largest angle.It was asking for the angle between both congruent legs of the isosceles triangle.

Whatisthis1

yeah it asked which was the angle between the congruent sides

nigcrunch

It never asked for the largest angle. It asked for the angle created by the two equal sides.

DMOC

Fourthed ... (what the other 3 people said)

wthalexis1

fifth-ed..

o1xDanny

TRIANGLE CALCULATOR Solves 4 Cases of Triangles - SSS - SAS - ASA - AAA

Sides; 10, 10, 5
Angles; 75.522, 75.522, 28.955

jamespotterz7

so the answer of this question is 29 right?

stix2400

the answer is 29, yep. 100%

blastie

why used law of cosines and complicated trigs -_-. Just divide the base into 2. (5/2). Then take cos-1(2.5/10). the angle should be 75.5. Double that, then 180-the result, it should give you the answer without wasting much of your time D:

nigcrunch

or you could use law of cosines by doing most of it in your head then punching a few numbers in on the calculator. =]. cos^-1(-175/-200)=28.955

o1xDanny

or, logically, Isosceles Triangle; Two Equal Angles > Smallest Angle; Meaning; TEA > 60 degrees each; or Smallest < 60 degrees, which only 29 fit. 180/3 = 60; ~ 75;75;30.

Jhnboy

draw a line from the 30 degree down to the side of 5

it splits the triangle into 2 right triangles.
Solved.

jamespotterz7

using law of cosines is way faster than thinking a whole bunch of stuff, that's what calculators are great for)

mabsjenbu123

crappp

I think I put 75 in my rush....