Pearson Algebra 2 Common Core, 2011
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Pearson Algebra 2 Common Core, 2011 View details
6. Solving Systems Using Matrices
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Exercise 45 Page 181

Use row operations to solve the matrix.

(8,2)

Practice makes perfect
We will first rewrite the system by substituting m and n for 1x and 1y, respectively.
4x+ 1y=1 & (I) 8x+ 4y=3 & (II)

(I), (II): Write fraction as a mixed number

4 1x+ 1y=1 8 1x+4 1y=3

(I), (II): 1/x= m, 1/y= n

4 m+ n=1 8 m+4 n=3
Now we can write the system as a matrix.

Matrix

To rewrite the system of equations as a matrix, we need to consider how the elements of the system relate to the elements of a matrix.
  • The equals signs in the system of equations are represented with a vertical bar in the matrix.
  • The coefficients of the variables form the columns on the left-hand side of the bar.
  • The constants form the column on the right-hand side of the bar.

Below we demonstrate this in a generalized form. a_(11)m+ a_(12)n=c_1 a_(21)m+ a_(22)n=c_2 ⇕ [ cc|c a_(11) & a_(12) & c_1 a_(21) & a_(22) & c_2 ] When each equation in the system is written in the same order, we can consider the coefficients of the variables and the constants. 4m+ 1n=1 8m+ 4n=3 Now that we have identified all of the variables and constants, we can place them in a matrix. [ cc|c 4 & 1 & 1 8 & 4 & 3 ]

Solving the Matrix

In order to solve the matrix, we will use row operations to obtain a matrix in the following form. [ cc|c 1 & 0 & a 0 & 1 & b ] This final matrix represents the solution of the system of equations, where m= a and n= b. Let's solve the matrix!
[ cc|c4 & 1 & 1 8 & 4 & 3 ]
[ cc|c8 & 2 & 2 8 & 4 & 3 ]
[ cc|c8 & 2 & 2 8- 8 & 4- 2 & 3- 2 ]
[ cc|c8 & 2 & 2 0 & 2 & 1 ]
[ cc|c8- 0 & 2- 2 & 2- 1 0 & 2 & 1 ]
[ cc|c8 & 0 & 1 0 & 2 & 1 ]
[ cc|c1 & 0 & 1/8 0 & 2 & 1 ]
[ cc|c1 & 0 & 1/8 0 & 1 & 1/2 ]
We have found that m= 18 and n= 12. Now we can find x and y. m=1/x=1/8 &⇒ x=8 [0.8em] n=1/y=1/2 &⇒ y=2 The solution of the system is the point (8,2).