Cosine rule question :S (1 Viewer)

[xJennax]

I'm trying to find the smallest angle in a triangle where the sides are:
11.9 , 16.3 and 17.5

I have done this..
Cos A = b² + c² - a²
2bc

= 16.3² + 17.5² - 11.9²
2 x 17.5 x 16.3

I've tried it a few times and get like 61,375.8... and 75 thousand or something.

Arrghhh what am I doing wrong? Maths is the worst subject ever lol

 

[bazookie]

did you use the inverse operation of cos after you did that?

doing what you just did, you will only find cos theta = (whatever number it comes out with.

you must then use the inverse operation of cos to find the angle, i.e SHIFT + COS + ANS.

also, make sure you are substituting the right numbers into the formula. Refer to your text book if you are not sure which ones to use.

 

[dazza 1]

isnt the smallest angle in a triangle the opposite to the smallest side?

 

[michael1990]

I got 41 degrees.
If its right, i will upload my working out.
Let me know.

 

[bazookie]

"isnt the smallest angle in a triangle the opposite to the smallest side?"

yes but she wants to find the actual value for it.


and i got 41 degrees aswell. I think she just forgot to inverse it.

 

[michael1990]

"isnt the smallest angle in a triangle the opposite to the smallest side?"

yes but she wants to find the actual value for it.

I think we may as well just ask her to post up the question.

OP - Could you post up the question please?
Scan it up?

 

[xJennax]

Thanks everyone.
I tried doing the inverse thing but it came up as an error.

I got 41 degrees.
If its right, i will upload my working out.
Let me know.

Yep it's 41 degrees, 2 minutes!

 

[xJennax]

I'll scan the question now. Appreciate your help guys.

 

[UNZPME]

I'm trying to find the smallest angle in a triangle where the sides are:
11.9 , 16.3 and 17.5

I have done this..
Cos A = b² + c² - a²
2bc

= 16.3² + 17.5² - 11.9²
2 x 17.5 x 16.3

I've tried it a few times and get like 61,375.8... and 75 thousand or something.

Arrghhh what am I doing wrong? Maths is the worst subject ever lol

i got 41 degrees...

try this
= 16.3² + 17.5² - 11.9² press equal divide it by 2 = divide by 17.5 = divide by 16.3 = then press second funtion cos and yo get 41 degree

 

[xJennax]

^ I'll try that now!

Here's the question, it's 4a.

 

[michael1990]

Okay so here is my working out.

 

[bazookie]

Cos theta = 17.5²+16.3²-11.9² / 2 x 17.5 x 16.3
do that then SHIFT + COS + Answer

=41 degrees

 

[UNZPME]

^ I'll try that now!

Here's the question, it's 4a.

did it work

 

[xJennax]

Yayyy I get it now! Thanks so much guys. =D

 

[xJennax]

did it work

yeah I tried everyone's working out and it all helped so ty.

 

[UNZPME]

yeah I tried everyone's working out and it all helped so ty.

nwzzz enytime

 

[snore]

don't forget to round to the nearest minute!!!

It's not just 41', it's 41'02'!