Answer:
dim L = dim U = 
Step-by-step explanation:
We can do it only for the lower-triangular matrices, the case of the upper-triangular matrices is similar. We might caracterice nxn the lower-triangular matrices, as the nxn matrices
such that the entry
if i<j.
Now let
and
be two lower triangular matrices, now if
for some 
then the entry
of C is equal to

Now, if i<j, it must hold that
. Therefore, if this is the case we must have that
and so we get that C is also a lower triangular matrix. This showa that L is closed under sum and scalar multiplcation, hence it is a linear subspace.
To find the dimension, note that all the entries of a lower-triangular matrix over the diagonal must be equal to zero. However, each entry of the matrix under the diagonal and in the diagonal might be any element of
, any entry that can be choosen add up to the dimension of L, we n such elemnts for the first column, (n-1) for the second column, (n-2) for the third column etc.... Therefore,

3+4 because they are both the same answer
It would be the last one to add up to 180 witch is a triangle or supplementary
<span />
Answer:
The first one towards the left, or the green triangle, would be 70 degrees.
The second one, or the one in the middle, would be 108 degrees.
The last one, or the yellow triangle, would be 65 degrees.