SOLUTION: If 2x - 10y = -16, and (x + y)/2 = -1, what is the value of xy? Would I use substitution in this case? x+y=-2 y=x-2 then 2x-10(x-2)=-16 2x-10x+20=-16 -8x=-36 x=36/8

Algebra ->  Expressions-with-variables -> SOLUTION: If 2x - 10y = -16, and (x + y)/2 = -1, what is the value of xy? Would I use substitution in this case? x+y=-2 y=x-2 then 2x-10(x-2)=-16 2x-10x+20=-16 -8x=-36 x=36/8      Log On


   

Question 855921: If 2x - 10y = -16, and (x + y)/2 = -1, what is the value of xy?
Would I use substitution in this case?
x+y=-2
y=x-2
then
2x-10(x-2)=-16
2x-10x+20=-16
-8x=-36
x=36/8
Answer by MathLover1(20850) About Me  (Show Source):
You can put this solution on YOUR website!
If 2x+-+10y+=+-16, and %28x+%2B+y%29%2F2+=+-1, what is the value of xy?
first, solve this system to find x and y:
2x+-+10y+=+-16...............eq.1
%28x+%2B+y%29%2F2+=+-1...............eq.2
______________________________________
start with
%28x+%2B+y%29%2F2+=+-1...............eq.2.............both sides multiply by 2
2%28x+%2B+y%29%2F2+=+-1%2A2
cross%282%29%28x+%2B+y%29%2Fcross%282%29+=+-2
x+%2B+y+=+-2 ............solve for x
x+=+-2-y....substitute in eq.1

2%28-2-y%29+-+10y+=+-16 ...............eq.1..solve for y
-4-2y+-+10y+=+-16
-4-12y++=+-16
-4%2B16++=12y
12++=12y
12%2F12++=y
+highlight%28y=1%29
now go back to x+=+-2-y and find x

x+=+-2-y....plug in y=1
x+=+-2-1
highlight%28x+=+-3%29
so, since highlight%28x+=+-3%29 and +highlight%28y=1%29 then the value of xy will be
xy=-3%2A1
highlight%28xy=-3%29