CCGPS Coordinate Algebra (2-4-13)

UNIT QUESTION: How do I justify and solve the solution to a system of equations or inequalities?Standard: MCC9-12.A.REI.1, 3, 5, 6, and 12

Today’s Question:When is it better to use substitution than elimination for solving systems?Standard: MCC9-12.A.REI.6

Solve Systems of Equations by

Graphing

Steps1. Make sure each equation is

in slope-intercept form: y = mx + b.

2. Graph each equation on the same graph paper.

3. The point where the lines intersect is the solution. If they don’t intersect then there’s no solution.

4. Check your solution algebraically.

y = 3x – 12y = -2x + 3

1. Graph to find the solution.

Solution: (3, -3)

2 2 82 2 4x yx y

2. Graph to find the solution.

Solution: (-1, 3)

2 52 1

y xy x

No Solution

3. Graph to find the solution.

22 3 9x yx y

Solution: (-3, 1)

4. Graph to find the solution.

Solution: (-2, 5)

5. Graph to find the solution.

52 1yx y

Types of Systems There are 3 different types of systems of linear

equations

3 Different Systems:1) Consistent-independent2) Inconsistent3) Consistent-dependent

Type 1: Consistent-independent A system of linear equations having

exactly one solution is described as being consistent-independent.y

x

The system has exactly one solution at the point of intersection

Type 2: Inconsistent A system of linear equations having no

solutions is described as being inconsistent.y

x

The system has no solution, the lines are parallel

Remember, parallel lines have the same slope

Type 3: Consistent-dependent A system of linear equations having an

infinite number of solutions is described as being consistent-dependent.y

x

The system has infinite solutions, the lines are identical

So basically…. If the lines have the same y-intercept b,

and the same slope m, then the system is consistent-dependent

If the lines have the same slope m, but different y-intercepts b, the system is inconsistent

If the lines have different slopes m, the system is consistent-independent

Solve Systems of Equations by Substitution

Steps1. One equation will have either x or y by

itself, or can be solved for x or y easily.2. Substitute the expression from Step 1 into

the other equation and solve for the other variable.

3. Substitute the value from Step 2 into the equation from Step 1 and solve.

4. Your solution is the ordered pair formed by x & y.

5. Check the solution in each of the original equations.

CW/HW1. 6 11 2. 2 3 1

2 3 7 1

3. 3 5 4. 3 3 35 4 3 5 17

5. 2 6. 5 74 3

y x x yx y y x

y x x yx y y x

y y xx y

18 3 2 12x y

HW

Graphing and Substitution WS