Problem 9.4 Given the system of equations -3x2 + 7x3 = 4 x1 + 2x2 - x3 = 0 5x1 -2 x2 = 3 (a) Compute the determinant. (b) Use Cramer’s rule to solve for the x’s. (c) Use Gauss elimination with partial pivoting to solve for the x’s. As part of the computation, calculate the determinant in order to verify the value computed in (a) (d) Substitute your results back into the original equations to check your solution.

- 3 x₂ + 7 x₃ = 3

x₁ + 2 x₂ - x₃ = 0

5 x₁ - 2 x₂ = 3

(a) I suppose this is asking for the determinant of the coefficient matrix.

Using a cofactor expansion along the first row, this reduces to

(b) Using Cramer's rule, we have

That is, solving for n-th variable consists of dividing [the determinant of the coefficient matrix with its n-th column replaced with the right side of the system, the numbers in boldface,] by [the determinant of the coefficient matrix].

Compute each determinant:

(expanding along the first column)

(again, along the first column)

(first column)

So, we get the solution

(c) Using elimination:

- 3 x₂ + 7 x₃ = 3

x₁ + 2 x₂ - x₃ = 0

5 x₁ - 2 x₂ = 3

Swap the first two equations:

x₁ + 2 x₂ - x₃ = 0

- 3 x₂ + 7 x₃ = 3

5 x₁ - 2 x₂ = 3

Add -5(equation 1) to equation 3:

x₁ + 2 x₂ - x₃ = 0

- 3 x₂ + 7 x₃ = 3

- 12 x₂ + 5 x₃ = 3

Add -4(equation 2) to equation 3:

x₁ + 2 x₂ - x₃ = 0

- 3 x₂ + 7 x₃ = 3

- 23 x₃ = -9

Multiply through equation 3 by -1/23:

x₁ + 2 x₂ - x₃ = 0

- 3 x₂ + 7 x₃ = 3

x₃ = 9/23

Add -7(equation 3) to equation 2:

x₁ + 2 x₂ - x₃ = 0

- 3 x₂ = 6/23

x₃ = 9/23

Multiply through equation 2 by -1/3:

x₁ + 2 x₂ - x₃ = 0

x₂ = -2/23

x₃ = 9/23

Add -2(equation 2) and equation 3 to equation 1:

x₁ = 13/23

x₂ = -2/23

x₃ = 9/23

step-by-step explanation:

given perimeter: 28cm

length: 9cm

atp,

2(l+w)=p of the reactangle

2(9+x)=28

18+2x=28

2x=28-18

x=10/2

x=5

therefore width is 5 cm