I was asked to solve this pair of simultanious equations using the substitution method:
2x+y=9
x-2y=7
This is what i did:
Rearrange x-2y=7 to make y the subject:
-2y=7-x
Y=3.5-0.5x
Sub in y:
2x+3.5-0.5x=9
1.5x+3.5=9
1.5x=5.5
X=3 2/3
Sub in x:
3 2/3 -2y=7
-2y=3 1/3
y=1 5/6
Am I right?
2007-11-28 07:37:27 · 7 answers · asked by Anonymous in Science & Mathematics ➔ Mathematics
Nope :(
2x+y=9
x-2y=7
2y = x - 7
y = x/2 - 7/2
2x + (x/2 - 7/2) = 9
5x/2 - 7/2 = 9
5x - 7 = 18
5x = 25
x = 5
y = x/2 - 7/2
y = 5/2 - 7/2
y = -2/2
y = -1
CHECK:
2x + y = 2(5) + (-1) = 9
x - 2y = 5 - 2(-1) = 5 + 2 = 7
2007-11-28 07:42:33 · answer #1 · answered by PeterT 5 · 1⤊ 0⤋
problem 1) when solving for y in -2y=7-x, you forgot to divide the negative, also when solving -2y=3 1/3.
My suggestions: solve for y in 2x+y=9, less division and less fractions.
Avoiding fractions whenever possible helps make fewer mistakes.
2007-11-28 15:42:10 · answer #2 · answered by alex h 2 · 0⤊ 0⤋
2x+y=9
x-2y=7 =>x=7+2y
2(7+2y)+y=9
14+4y+y=9
x=7+2y
14+5y=9
x=7+2y
5y=9-14
x=7+2y
5y=-5
x=7+2y
y= -1
x=7+2(-1)
y= -1
x=5
this is the most "elegant" solution using the substitution method
2007-11-28 15:45:16 · answer #3 · answered by YAHOO USER 1 · 0⤊ 0⤋
-2y = 10 / 3,
multiply through by -1,
2y = - 10 / 3,
y = - 5 / 3.
2007-11-28 15:58:53 · answer #4 · answered by BB 7 · 0⤊ 0⤋
2x+4y=14
2x+y=9
3y = 5
y=5/3
2007-11-28 15:43:19 · answer #5 · answered by eyeguy 2 · 0⤊ 0⤋
when you divided by -2 to find y, it should be
y= neg 3.5 plus .5x
2007-11-28 15:40:13 · answer #6 · answered by mom 7 · 0⤊ 0⤋
no ur not i don't know how but everyone here say you r wronge
2007-11-28 15:40:27 · answer #7 · answered by Rebecca T 1 · 0⤊ 2⤋