Download 01/09/12 _ 01/10/12: Solving SOE`s by Elimination pt. 2/ Linear

01/09/12 _ 01/10/12: Solving SOE’s by Elimination pt. 2/ Linear Inequalities
1. From now on, write table number on things to expedite returns.
2. Warm up: Three pencils and a jumbo eraser cost $1.24. Five pencils and a jumbo eraser cost $1.82. No prices include
tax. In cents, what is the cost of a pencil?
a. 5x + y = 1.82
b. 3x + y = 1.24 subtract
c. 2x
= .58
d. x = .29
3. Review warm up and pass back/review quicky quiz #2
Ex 1:
0) Both are standard form
1) Choosing y because just have to multiply second equation by 2 to get opposite coefficients
2) 2nd by 2  4x + 4y = 42
3)
3x – 4y = 14
+ 4x + 4y = 42
7x
= 56
x
=8
4) 3(8) – 4y = 14  y = 2.5
Ex 2:
0) Both are standard form
1) Doesn’t matter which one… just about the same amount of work for both… so I’ll pick x
2) Need to multiply first by 3 and second by –5 to get opposite coefficients of x
5x – 6y = 12  15x – 18y = 36
3x – 5y = 24  -15x + 25y = -120
3)
15x – 18y = 36
+ -15x + 25y = -120
7y = -84
y = -12
4) 5x –6(-12) = 12  x = -12
Note, if you get a fractional answer and really don’t want to substitute it back into one of the equations to find the other
number in the solution, you can always eliminate again, this time choosing to eliminate the other variable
LINEAR INEQUALITIES: Group activity
1) Solutions for #2… y<-1/3x + 6 and y > 4/3x-2
SIGMA #3: 30 minutes
Quicky Quiz: Four pens and a two pencils cost $1.28. Seven pens and two pencils cost $2. No prices include tax. In cents,
what is the cost of a pen?
 7x + 2y = 2.00
 4x + 2y = 1.28 subtract
 3x = 0.72
 x = 0.24
HW 3.3: Solving SOES pt.2
 Pgs 454- 455: 5, 7, 11, 13, 21, 23, 27, 31, 33, 37
Quiz 3.1 on 1/11 or 1/12