Problem with two unknowns

SILVER

New member
Joined
Jan 27, 2011
Messages
18
here is a problem i don't get:
2x+3y=7
-10x-3y=25
its a problem with two unknowns and the answer is x=-4, y=5. I started by adding the two together and got -12x=32 but when i divided that i got -0.37 and the answer ix=-4.HELP!
 
J

JeffM

Guest
SILVER said:
here is a problem i don't get:
2x+3y=7
-10x-3y=25
its a problem with two unknowns and the answer is x=-4, y=5. I started by adding the two together and got -12x=32 but when i divided that i got -0.37 and the answer ix=-4.HELP!
Does 2x + (-10x) = -12x?

I do wonder as well how you divided 32 by -12 and got -0.37.

Need to be more careful
 

SILVER

New member
Joined
Jan 27, 2011
Messages
18
2x+(-10x)=-32 does'nt it? when i divided 32 by -12 i got -2.66. How do i get -4?
 

Denis

Senior Member
Joined
Feb 17, 2004
Messages
1,465
SILVER said:
2x+(-10x)=-32 does'nt it? when i divided 32 by -12 i got -2.66. How do i get -4?
C'mon Silver...
2x + (-10x) = 32 : NOT -32
-8x = 32
 

Mrspi

Senior Member
Joined
Dec 17, 2005
Messages
2,128
SILVER said:
2x+(-10x)=-32 does'nt it? when i divided 32 by -12 i got -2.66. How do i get -4?
Why would you divide by -12? 2x + (-10x) is not -12x (it isn't 12x, either). It looks like you may need to review addition of signed numbers. Here's a website you can start with (there are many others available online):

http://www.purplemath.com/modules/negative2.htm
 

SILVER

New member
Joined
Jan 27, 2011
Messages
18
thanks,sorry careless mistake my brain does'nt seem to be working today
 
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