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

Thanks in advance guys (or girls.)