3x-2y=9
4x+7y=-17
How would you solve this system
2007-02-07 01:36:10 · 6 answers · asked by danielle 2 in Science & Mathematics ➔ Mathematics
Multiply the first equation by 7 and the second equation by 2:
21x-14y=63
8x+14y=-34
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29x=29
x=1
21(1)-14y=63
21-14y=63
-14y=42
y=-3
The solution set is (1,-3)
Check:
3(1)-2(-3)=9
3+6=9
9=9
4(1)+7(-3)=-17
4-21=-17
-17=-17
2007-02-07 01:44:54 · answer #1 · answered by Anonymous · 5⤊ 0⤋
3x - 2y 9- - - - - - - - -Equation 1
4x + 7y = - 17- - - - - -Equation 2
- - - - - - - - - -
Multiply equation 1 by 7 and multiply equation 2 by 2.
3x - 2y = 9
7(3x) - 7(2y) = 7(9)
21x - 17y = 63
- - - - - - - -- --
4x + 7y = - 17
2(4x) + 2(7y) = - 2(17)
8x + 14y = - 34
- - - - - - - -
21x - 14y = 63
8x + 14y = - 34
- - - - - - - - - -
29x = 29
29x/29 = 29/28
x = 29/29
x = 1
The answer is x = 1
Insert the x value into equation 2
- - - - - - - - - - - - - - - - - - - - - -
4x + 7y = - 17
4(1) + 7y = - 17
4 + 7y = - 17
4 + 7y - 4 = - 17 - 4
7y = - 21
7y/7 = - 21/7
y = - 21/7
y = - 3
The answer is y = - 3
Insert the y value into equation 2
- - - - - - - - - - - - - - - - - - - - - - -
Check for equation 2
4x + 7y = - 17
4(1) + 7(- 3) = - 17
4 + (- 21) = - 17
4 - 21 = - 17
- 17 = - 17
- - - - - - - - - -
Check for equation 1
3x - 2y = 9
3(1) - 2(- 3) = 9
3 - (- 6) = 9
3 + 6 = 9
9 = 9
- - - - - - - - - - - --
The solution set { 1, - 3 }
- - - - - - - - - - -s-
2007-02-07 10:23:01 · answer #2 · answered by SAMUEL D 7 · 1⤊ 0⤋
Multiply the first equation (3x-2y=9)by 4, this will yield
12x-8y=36
Multiply the first equation (4x+7y=17)by 3 this will yield
12x+21y=-51
Subtracting the first equation from the second.
21y-(-8y)+12x-12x=-51-36
29y=-87
Therefore y=- 3
From 3x-2y=9, x can be calculated.
3x-(2*-3)=9
3x+6=9
3x=3
therefore x=1
2007-02-07 09:52:14 · answer #3 · answered by The exclamation mark 6 · 1⤊ 0⤋
Let 3x-2y=9 be eq.1
Let 4x+7y=-17 be eq.2
Multiply eq. 1 by 4
Multiply eq. 2 by 3
Therefore, you will get:
12x-8y=36 ------> eq.1a
12x+21y=-51----->eq.2a
then subtract 2a from 1a, you get:
-29y= 87
y= -87/29
y = -3
Substitue value for y in eq.1
3x- 2(-3) = 9
3x+6 = 9
3x = 9-6
3x=3
x= 1
so y=-3 and x=1
2007-02-07 09:56:00 · answer #4 · answered by MowGI M 2 · 1⤊ 0⤋
3x - 2y = 9-------------Multiply by 7
4x + 7y = -17---------Multiply by 2
21x - 14y = 63
8x + 14y = -34
29x = 29
x = 1
Now 4x + 7y = - 17
so 4 + 7y = - 17
7y = -21
y = - 3
Solution is x = 1, y = -3
2007-02-07 10:14:31 · answer #5 · answered by Como 7 · 1⤊ 0⤋
x=(9+2y)/3
substitute it in second eqn.
x=1
y=-3/2
2007-02-07 09:41:38 · answer #6 · answered by jonny k 3 · 1⤊ 2⤋