# Do Now Graph x = -2 x + 4y = 12.

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Do Now Graph x = -2 x + 4y = 12

Section 3.1 Solving Systems using tables and graphs
What is a System of Equations? Solving Linear Systems – The Graphing Method Consistent Systems – one point (x,y) solution Inconsistent Systems – no solution Dependant Systems – infinite solutions Solving Equations Graphically

Concept: A System of Linear Equations
Any pair of Linear Equations can be a System A Solution Point is an ordered pair (x,y) whose values make both equations true When plotted on the same graph, the solution is the point where the lines cross (intersection) Some systems do not have a solution

Why Study Systems of Equations?
We will study systems of 2 equations in 2 unknowns (usually x and y) The algebraic methods we use to solve them will also be useful in higher degree systems that involve quadratic equations or systems of 3 equations in 3 unknowns

A “Break Even Point” Example. A \$50 skateboard costs \$12. 50 to build,
A “Break Even Point” Example A \$50 skateboard costs \$12.50 to build, once \$15,000 is spent to set up the factory: Let x = the number of skateboards f(x) = x (total cost equation) g(x) = 50x (total revenue equation)

Using Algebra to Check a Proposed Solution
Is (3,0) also a solution?

Estimating a Solution using The Graphing Method
Graph both equations on the same graph paper If the lines do not intersect, there is no solution If they intersect: Estimate the coordinates of the intersection point Substitute the x and y values from the (x,y) point into both original equations to see if they remain true equations

Approximation … Solving Systems Graphically

Practice – Solving by Graphing
Consistent: (1,2) y – x = 1  (0,1) and (-1,0) y + x = 3  (0,3) and (3,0) Solution is probably (1,2) … Check it: 2 – 1 = 1 true 2 + 1 = 3 true therefore, (1,2) is the solution (1,2)

Practice – Solving by Graphing
Inconsistent: no solutions y = -3x  (0,5) and (3,-4) y = -3x – 2  (0,-2) and (-2,4) They look parallel: No solution Check it: m1 = m2 = -3 Slopes are equal therefore it’s an inconsistent system

Practice – Solving by Graphing
Consistent: infinite sol’s 3y – 2x = 6  (0,2) and (-3,0) -12y + 8x = -24  (0,2) and (-3,0) Looks like a dependant system … Check it: divide all terms in the 2nd equation by -4 and it becomes identical to the 1st equation therefore, consistent, dependant system (1,2)

Summary of Section 3.1 Solve Systems by Graphing Them Together
Graph neatly both lines using x & y intercepts Solution = Point of Intersection (2 Straight Lines) Check by substituting the solution into all equations Cost and Revenue lines cross at “Break Even Point” A Consistent System has one solution (x,y) An Inconsistent System has no solution The lines are Parallel (have same slope, different y-intercept) A Dependent System happens when both equations have the same graph (the lines have same slope and y-intercept)

Homework pg Homework: P. 138 #7,9,13,14,29,31,33,38,39,40,41,53,54 Challenge: #48

What Next? Present Section 3.2 Solving Systems Algebraically

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