Date post: | 21-Mar-2017 |
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3x + 2y = 172x – 5y = 5
3x + 2y = 17 X5→ 15x + 10y = 852x – 5y = 5 X2→ 4x – 10y = 10
Add 19x = 95 x = 5
Consider two lines
simultaneous equations
15 + 2y = 17y = 1
POI (5 , 1)
(the Elimination Method)
Lines usually written:
y = 5x + 1y = 3x + 7
So 5x + 1 2x + 1 = 7
2x = 6 x = 3
Point of intersection (3 , 16)
Must be the same
y = 5(3) +1 = 16
Known as
y=y tactic= 3x + 7
£y £y
Using y = y
Find the points of intersection, for these pairs of lines:
1. y = 5x – 3 and y = 2x + 122. y = 7x + 8 and y = x +203. y = -2x + 8 and y = 2x + 124. y = 5x + 3 and y = 24 – 2x
(5,22)(2,22)
(-1,10)
(3,18)
y = 2x5x + 3y = 22
Replace y with 2x
5x + 3 = 225x + 6x = 22
11x = 22 x = 2 x = 2 y = 2(2)
= 4Intersection (2 , 4)
(2x)y
Handy!
substitution
y = 4x + 33x + 2y = 17
Replace y with 4x + 3
3x + 2 = 173x + 8x + 6 = 17
11x + 6 = 17 11x = 11 x = 1 y = 4 (1) +3
= 7Intersection (1 , 7)
(4x+3)y
substitution
Using Substitution
Find intersections of these lines:1. x = 8 and
2y + 4x = 422. y = 8 and
3y = 2x + 43. y = 2x and
2y + 3x = 28
Using Substitution
Find intersections of these lines:1. x = 8 and
2y + 4x = 42 (8 , 5)2. y = 8 and
3y = 2x + 43. y = 2x and
2y + 3x = 28
Using Substitution
Find intersections of these lines:1. x = 8 and
2y + 4x = 42 (8 , 5)2. y = 8 and
3y = 2x + 4 (10 , 8)3. y = 2x and
2y + 3x = 28
Using Substitution
Find intersections of these lines:1. x = 8 and
2y + 4x = 42 (8 , 5)2. y = 8 and
3y = 2x + 4 (10 , 8)3. y = 2x and
2y + 3x = 28 (4 , 8)
Points of Intersection
Can use• Simultaneous Equations• y = y• Substitution
Depends on way lines are given
Ex 3 2x + 3y = 13 y = 2x – 1
Substitute y= 2x – 1 into*2x + 3(2x – 1) = 132x + 6x – 3 = 13 8x = 16 x = 2 y = 2 (2) – 1 = 3(from second equation)Intersection (2 , 3)
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