Plzzzzzz helppppp asappppp ***will mark brainliest *****

Show that the sets of upper-triangular and lower-triangular matrices are subspaces of F n,n . Call them U and L respectively. Wh

soldi70 [24.7K]

Answer:

dim L = dim U = $\frac{n(n+1)}{2}$

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 $A=(a_{ij})$ such that the entry $a_{ij}=0$ if i<j.

Now let $A=(a_{ij})$ and $B=(b_{ij})$ be two lower triangular matrices, now if

$C=A+\lambda B$ for some $\lambda \in \mathbb{F}$

then the entry $c_{ij}$ of C is equal to

$c_{ij}=a_{ij}+\lambda b_{ij}$

Now, if i<j, it must hold that $a_{ij}=0 \quad \text{and} \quad b_{ij}=0$ . Therefore, if this is the case we must have that $c_{ij}=0$ 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 $\mathbb{F}$ , 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,

$\dimL=n+(n-1)+(n-2)+...+2+1=\dfrac{n(n+1)}{2}$

5 0

3 years ago

-15 as the ratio of 2 intergers

agasfer [191]

Answer:

45/-3=-15

Step-by-step explanation:

A negative integer is a negative whole number that is the opposite of a counting number. It is simply an integer less than 0.

7 0

3 years ago

You have a pool that measures 15 yards by 20 yards. You want to build a deck around all four sides of the pool, and you want to

madam [21]

x = 1.75 yards. Hope this helps!! <3

5 0

3 years ago

A chef is going to use a mixture two different brands of Italian dressing the first spring and days 5% vinegar the second brain

Temka [501]

I guess the chef is making the mixture for the sheriff... Let x be the amount of dressing with 5% vinegar that is required, and y the amount of 15% vinegar dressing (both amounts in mL).

The sheriff wants 390 mL of the mixed dressing, so that

x + y = 390

x mL of the 5% dressing contains 0.05x mL of vinegar, while y mL of the 15% dressing contains 0.15y mL of vinegar. The resulting mixture should have a concentration of 9% vinegar, so that it contains 0.09 (390 mL) = 35.1 mL of vinegar. This means

0.05x + 0.15y = 35.1

Solve for x and y :

y = 390 - x

0.05x + 0.15 (390 - x) = 35.1

0.05x + 58.5 - 0.15x = 35.1

23.4 = 0.10x

x = 234

y = 156

7 0

3 years ago

Need help 3x+10y=-10

Genrish500 [490]

Answer: 10 + 10 = 21

dont ask how

7 0

3 years ago