Let U be a matrix where u_ij = 0 if i > j, and L be a matrix where l_ij = 0 if i < j. (a) U is called an upper triangular matrix and L is a lower tri-angular matrix. Explain why.
(b) Prove or disprove: The sum of two upper triangular matrices is an upper triangular matrix.
(c) Prove or disprove: The product of two upper triangular matrices is an upper triangular matrix.

A) U is called an upper triangular matrix because all entries below the principal diagonal element are zeros ( 0 )   since Uij = 0 if i >j  also

L is a lower triangular matrix because all entries above the principal diagonal element are zero ( 0 )

B) sum of two upper triangular matrices = upper triangular matrix.

C) product of two upper triangular matrices = upper triangular matrix

Step-by-step explanation:

A) U is called an upper triangular matrix because all entries below the principal diagonal element are zeros ( 0 )   since Uij = 0 if i >j  also

L is a lower triangular matrix because all entries above the principal diagonal element are zero ( 0 ) since Lij = 0  if i < j

B) To prove that sum of two upper triangular matrices

attached below

C) Prove or disprove that product of two upper triangular matrices is an upper triangular matrix

attached below

It equals 1373.5 that’s the solution

The answer is a 5/20 because if u add all of the marbles there are 20 and there are 5 red marbles so 5/20 is the answer mark as brainliest