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jxharmon

Member

Registered: 2007-01-08

Posts: 104

substitution confusion please help

solve the system by substitution

3x + 6y =o; x=2/3; 3(2/3) +6y =0; 2+ 6 = ) confused???

3x - y = -7 ; x + y = -9; y= -x-9;  3x -x = -7; 2x = -7; x = -7/2 now I'm confused again what in the world am I doin??

John E. Franklin

Member

Registered: 2005-08-29

Posts: 3,588

Re: substitution confusion please help

You almost got this one done, just forgot to write down the y with the 6.
Here's you:
3x + 6y =o; x=2/3; 3(2/3) +6y =0; 2+ 6 = )
3x + 6y =o; x=2/3; 3(2/3) +6y =0; 2+ 6y = 0; 6y = -2; y = -1/3

And other one:
You said:
3x - y = -7 ; x + y = -9; y= -x-9;  3x -x = -7; 2x = -7; x = -7/2 now I'm confus
3x - y = -7 ; x + y = -9; y =-x-9;  3x + x + 9 = -7; 4x = -16; x = -4; y = -(-4) - 9; y = -5

That should clear things up a bit. bye.

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igloo myrtilles fourmis

jxharmon

Member

Registered: 2007-01-08

Posts: 104

Re: substitution confusion please help

thanks guess I wasn't wotching close enough; could the first one also be done by addition?? if so how does it work??

Last edited by jxharmon (2007-02-10 08:03:11)