Exercise 4 Page 274

When solving a system of equations using the Substitution Method, there are three steps.

1. Isolate a variable in one of the equations.
2. Substitute the expression for that variable into the other equation and solve.
3. Substitute this solution into one of the equations and solve for the value of the other variable. For this exercise, y is already isolated in one equation, so we can skip straight to solving!
   y= 12x+4 & (I) x-y=8 & (II)

   Substitute

   (II):y= 1/2x+4

   y= 12x+4 x-( 12x+4)=8

   Distr

   (II): Distribute -1

   y= 12x+4 x- 12x-4=8

   ▼

   (II): Simplify left-hand side

   NumberToFrac

   (II): a = 2* a/2

   y= 12x+4 2x2- 12x-4=8

   MoveRightFacToNumOne

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

   y= 12x+4 2x2- x2-4=8

   SubFrac

   (II): Subtract fractions

   y=1/2x+4 x2-4=8

   AddEqn

   (II): LHS+4=RHS+4

   y= 12x+4 x2=12

   MultEqn

   (II): LHS * 2=RHS* 2

   y= 12x+4 x2* 2=12* 2

   ▼

   Multiply

   FracMultDenomToNumber

   (II): a/2* 2 = a

   y= 12x+4 x=12* 2

   Multiply

   (II): Multiply

   y= 12x+4 x=24

   Great! Now, to find the value of y, we need to substitute x=24 into either one of the equations in the given system. Let's use the first equation.

   y= 12x+4 x=24

   Substitute

   (I):x= 24

   y= 12( 24)+4 x=24

   MoveRightFacToNumOne

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

   y= 242+4 x=24

   CalcQuot

   (I): Calculate quotient

   y=12+4 x=24

   AddTerms

   (I): Add terms

   y=16 x=24

   The solution, or point of intersection, to this system of equations is the point (24,16).