Unit 4A Day 4 - solving systems by substitution

What is the first step in solving a system by Substitution?

• Make sure both equations are in standard form.
• Make sure at least one equation is solved for one variable.
• Make sure both equations are in slope-intercept form.
• Make sure both equations can be solved.

Solve this system of equations. 
y = 2x + 1
y = 4x - 1

• (1,3)
• (-1,-3)
• (-1,3)
• (3,1)

Solve the system by substitution.
 
5x + 4y= −14
y =  −7x  −  15 

• (-2, -1)
• (1, -2)
• (-2, 1)
• (-1, -2)

Solve:
y = 2x -11
-3y = -6x -15

• (-1.5,-4)
• (1.5,4)
• No solution (parallel lines)
• Infinitely many solutions

x + 2y = 2
x = -4y + 2

• (-3, 0)
• (0, 2)
• (-3, -2)
• (2, 0)

x - 3y = -13
4x + 2y = 4

• (1, 4)
• (-1, -4)
• (-1, 4)
• (1, -4)

y = -6x + 5
-2x + y = 5

• (-3, -6)
• (-6, 3)
• (0, 5)
• (-3, 5)

x = -3y - 8
x - 2y = -3

• (5, -1)
• (-5, 1)
• (-5,-1)
• (1,-5)

3x + 2y = 8
-x + y = -11

• (-5,6)
• (6,-11)
• (-6,-5)
• (6,-5)

If a system of equations has no solution, what does the graph look like? 

• intersecting lines
• parallel lines
• skew lines
• intersecting lines