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# math problem (linear algebra)

please provide the procedure....I will give more mark if you think 20 is not enough...however, I only have 100 marks left...please help me..

Question 4: Write the following system of linear equations in the form Ax =b and

solve it.

x−y + 4z = 17

x+3y+ = −11

−6y + 5z = 40.

.Question 6: The trace of a square matrix of order n, A = [aij ]1=<i,j=<n, is defined to

be the sum of main diagonal entries of A. That is Tr(A) = a11 +a22 +· · · ann. Prove

that if A and B square matrices of order n, then Tr(AB) = Tr(BA).

### 1 Answer

- 匿名Lv 61 decade agoFavorite Answer
x+3y+ = −11? 要加什麼z?

2009-02-05 14:41:17 補充：

Question 4:

In the form of Ax = b:

[1 -1 4][x] [17 ]

[1 3 0 ][y]=[-11]

[0 -6 5][z] [40 ]

Solve:

[1 -1 4 17]

[1 3 0 -11]

[0 -6 5 40]

row2 = row1-row2

[1 -1 4 17]

[0 -4 4 28]

[0 -6 5 40]

row2 = row2/(-4)

[1 -1 4 17]

[0 1 -1 -7]

[0 -6 5 40]

row1 = row1+row2, row3 = row2*6+row3

[1 0 3 10 ]

[0 1 -1 -7]

[0 0 -1 -2]

row3 = row3/(-1)

[1 0 3 10 ]

[0 1 -1 -7]

[ 0 0 1 2 ]

row1 = row1-row3*3, row2 = row2+row3

[1 0 0 4 ]

[0 1 0 -5]

[0 0 1 2 ]

So, x = 4, y = -5, z = 2.

(p.s. You can use inverse of A to solve this problem as well)

Question 6:

See part (a) of http://lrg103.zorpia.com/0/4945/31653147.2d1a12.jp...

Source(s): http://lrg103.zorpia.com/0/4945/31653147.2d1a12.jp... (by EMK)