http://www.ck12.org Chapter 8. Systems and Matrices
The point(− 1 ,^15 )is the point of intersection between these two curves.
Concept Problem Revisited
Plan A costs $40 per month plus $0.10 for each minute of talk time.
Plan B costs $25 per month plus $0.50 for each minute of talk time.
If you want to find out when the two plans cost the same, you can represent each plan with an equation and solve the
system of equations. Letyrepresent cost andxrepresent number of minutes.
y= 0. 10 x+ 40
y= 0. 50 x+ 25First you put these equations in standard form.
x− 10 y=− 400
x− 2 y=− 50Then you scale the second equation by -1 and add the equations together and solve fory.
− 8 y=− 350
y= 43. 75To solve forx, you can scale the second equation by -5, add the equations together and solve forx.
− 4 x=− 150
x= 37. 5The equivalent costs of plan A and plan B will occur at 37.5 minutes of talk time with a cost of $43.75.
Vocabulary
Asystem of equationsis two or more equations.
Standard formfor the equation of a line isAx+By=C.
Toscale an equationmeans to multiply every term by a constant.
Guided Practice
- Solve the following system using elimination:
20 x+ 6 y=− 32
18 x− 14 y= 10