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 46 Page 181

Use row operations to solve the matrix.

(5,-10)

Practice makes perfect
We will first rewrite the system by substituting m and n for 1x and 1y, respectively.
4x- 2y=1 & (I) 10x+ 20y=0 & (II)

(I), (II): a/b=a* 1/b

4 1x-2 1y=1 10 1x+20 1y=0

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

4 m-2 n=1 10 m+20 n=0
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 -2n=1 10m+ 20n= Now that we have identified all of the variables and constants, we can place them in a matrix. [ cc|c 4 & -2 & 1 10 & 20 & ]

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 & -2 & 1 10 & 20 & 0 ]
[ cc|c4 & -2 & 1 1 & 2 & 0 ]
[ cc|c4+ 1 & -2+ 2 & 1+ 0 1 & 2 & 0 ]
[ cc|c5 & 0 & 1 1 & 2 & 0 ]
[ cc|c1 & 0 & 1/5 1 & 2 & 0 ]
[ cc|c1 & 0 & 1/5 1- 1 & 2- 0 & 0- 1/5 ]
[ cc|c1 & 0 & 1/5 0 & 2 & -1/5 ]
[ cc|c1 & 0 & 1/5 0 & 1 & -1/10 ]
We have found that m= 15 and n=- 110. Now we can find x and y. m&=1/x= 1/5 ⇒ x=5 n&=1/y=-1/10 ⇒ y=-10 The solution of the system is the point (5,-10).