Solve the following systems:
x+y=7
x-y=-11
2007-06-05 02:12:33 · 9 answers · asked by marshymoe 2 in Science & Mathematics ➔ Mathematics
In this case, I would add the two equations together. This is becuase you have a +y in one and a -y in the other. This will allow you to quickly get to an answer for x.
So, by adding the equations, you get:
2x = -4
Now, divide by 2 on both sides in order to isolate x and you get:
x = -4/2 = -2
Now, substitute that into the first equation, and you get:
-2+y = 7
Add 2 to both sides and you get:
y=9
Check your answer by subsituting these values into the second equation:
-2-9 = -11, -11=-11 (you have the right answers)
2007-06-05 02:18:28 · answer #1 · answered by Anonymous · 0⤊ 0⤋
The easiest way to do this to simply add them up - like this
x + y = 7 +
x - y = -11
________
2x = -4 (or in other words , x = -2 & y = 9)
For substitution, you could do this
using the first equation, x = 7- y ...(1)
put this in x - y = -11,so u get
(7 - y) -y = -11 (using 1, x = 7- y)
which is the same as 2y = 18 (after you transpose the terms correctly with their right signs) , also same as y = 9 from which you can easily get x = -2
that should solve it
2007-06-05 09:24:15 · answer #2 · answered by Purvabh S 1 · 0⤊ 0⤋
If both the equations refer to the same x and y, it is possible to solve.
x+y = 7 and x-y=-11 or x = y - 11
Substituting that in the first equation
y-11 + y = 7 or 2y = 18 and y = 9
So, x is y - 11 = 9 - 11 = - 2
x = -2 and y = 9
2007-06-05 09:21:20 · answer #3 · answered by Swamy 7 · 0⤊ 0⤋
Taking first equation:
x+y=7
x=7-y ............. (1)
Replacing (1) in equation x-y=-11
(7-y)-y=-11
7-y-y=-11
7-2y=-11
-2y=-11-7
-2y=-18
y=9........(2)
Replacing (2) in equation x+y=7
x+9=7
x=7-9
x=-2
Therefore, x=-2,y=9
This method of solving is called substitution.
2007-06-05 09:21:16 · answer #4 · answered by nivik 3 · 0⤊ 0⤋
add the equations
gives
2x=7+11=18 so x=9
the substitute x=9 in the first equation (or 2nd if you like)
9+y=7 so y=7-9= -2
answer is x=9,y= -2
2007-06-05 09:22:17 · answer #5 · answered by The Wolf 6 · 1⤊ 0⤋
Pretty easym, this one.
From the first equation, x = 7-y.
Substitute it in the second.
(7-y)-y=-11
7-2y=-11
2y=18
y=9
x=7-y=7-9=-2
So x=-2, y=9.
You could also solve it by adding the 2 equations, you would've got 2x = -4, thus x=-2.
2007-06-05 09:20:32 · answer #6 · answered by --sv-- 2 · 0⤊ 0⤋
First, use the elimination method.
x + y = 7
- x - y = -11
-------------------------
2y = 18
------------
2 2
y = 9
you now have the value of y. now, solve for x:
x + y = 7 ---> x + 9 = 7
x = 7 - 9
x = -2
And the values are: (-2,9)
2007-06-05 09:26:34 · answer #7 · answered by genius_06 3 · 0⤊ 0⤋
x+y=7
x-y=11
add2x=18,x=9
y=-2
2007-06-05 09:21:24 · answer #8 · answered by Anonymous · 0⤊ 0⤋
x = 7 -y ...............(1)
put it in the second one
7-y-y=11
7-2y=11
-2y=4
y=-2
put it in (1)
x= 7 - (-2) = 9
2007-06-05 09:22:18 · answer #9 · answered by mR.qUESTiON?? 2 · 0⤊ 0⤋