# Finding an angle within this triangle

• Oct 21st 2012, 09:52 AM
Corpsecreate
Finding an angle within this triangle
Hi,

All variables given in blue are known values. I am trying to calculate the angle X in terms of the variables I know. How can I do this?

http://img100.imageshack.us/img100/2673/trih.jpg
• Oct 21st 2012, 10:05 AM
Soroban
Re: Finding an angle within this triangle
Hello, Corpsecreate!

Quote:

All variables given in blue are known values.
I am trying to calculate the angle X in terms of the variables I know.

http://img100.imageshack.us/img100/2673/trih.jpg

The sum of the (interior) angles of a triangle is always equal to 180o.

Hence: . $A + B + (C + X) \;=\;180$

Got it?
• Oct 21st 2012, 10:07 AM
BobP
Re: Finding an angle within this triangle
You can calculate the angle between the side $b$ and the horizontal, add $X$ to that and you have the angle $C.$
• Oct 21st 2012, 07:09 PM
Corpsecreate
Re: Finding an angle within this triangle
Quote:

Originally Posted by Soroban
Hello, Corpsecreate!

The sum of the (interior) angles of a triangle is always equal to 180o.

Hence: . $A + B + (C + X) \;=\;180$

Got it?

Angle $C$ is the entire interior angle, not just the angle up to the horizontal. $A + B + C$ will give $180$, $A + B + (C + X)$ will give a number larger than $180$.

Quote:

Originally Posted by BobP
You can calculate the angle between the side $b$ and the horizontal, add $X$ to that and you have the angle $C.$

The angle side $b$ makes with the horizontal is $A + phi$, I dont see how adding $X$ to this angle would give me angle $C$?

NVM: Question has been solved!
• Oct 22nd 2012, 01:53 AM
BobP
Re: Finding an angle within this triangle
Quote:

The angle side $b$ makes with the horizontal is $A + phi$, I dont see how adding $X$ to this angle would give me angle $C$?
NVM: Question has been solved!
The angle referred to is the complement of the one you state, that is, $180 - (A+\phi).$

This will equal the angle below the horizontal at $C.$ Add $X$ and you get $C.$

BTW., some labels on the diagram would have helped.