# Thread: Finding the area of a triangle using vector projections.

1. ## Finding the area of a triangle using vector projections.

Wasn't for sure if this should be posted here or in the Linear Algebra forum. It's in my Linear Algebra class but is still fairly basic stuff I think..

I can't seem to get the correct answer for question 47 from this page and can't figure out what I am doing wrong. I tried using the formula given and also tried using the basic 1/2bh (which gives the same formula):

Here's my work (a bit all over the place but should be readable, any questions ask.)

My final answer would have been $1/2sqr(6)sqr(11/2)$ but simplified or whatever. The answer in the back is $1/2sqr(45)$ though and I can't seem to find my mistake.

Thanks in advance guys (or girls.)

2. Found a mistake in my work. The Projection of AC onto AB should actually be -1/3 in the z frame not 1/3. However I am still getting the wrong final answer. Allowing that to substitue changes the norm of AB subtract the projection to be 7/3. Still gives me the wrong answer of $7/6sqr(6)$

3. Nevermind on that last post my math is all over the map but I still can't seem to find the answer.
1/2sqr(49) is the latest/closest answer yet. still looking for little mistakes.

4. Originally Posted by Cheesehunk
Nevermind on that last post my math is all over the map but I still can't seem to find the answer.
1/2sqr(49) is the latest/closest answer yet. still looking for little mistakes.
Can you type up your work?

It is hard to read off the paper.