posted by on .

x+2y=3
5x+4y=8

I isolated x+2y=3 to make: x=3-2y
then i began to sub in equation one with equation two:
5x+4y(3-2y)=8
5x+12-8y=8

after that i began to try to solve the equation but my answers were not correct. any help would be greatly appreciated!

You are substituting for y instead of x
Besides that you were still keeping the y as well.

5(3-2y) + 4y = 8
15 - 10y + 4y = 8
-6y = -7
y = 7/6

then in x = 3-2y
x = 3-14/6 = 2/3

x = 2/3 , y = 7/6

i understand how you got the answer i just don't get why i don't put 5x+4y before the equation because i have been for all the other ones and i got those ones right..

for example this one:
6x+5y= 7
x-y= 3
i isolated the second equation into y=3+x

so: 6x+5y(3+x)=7
6x+15+5x=7
6x+5x-15+15=7+15
11/11= 22/11
x=2

then i subbed in the other equation..
6(2)+5y=7
12+5=7-12
5y/5= -5/5
y= -1

and i checked my answer and it was correct.
i just don't understand what i'm doing wrong for the equation.. because i keep thinking the full equation must go first not separate it.

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