View Full Version : How to find x

resqswmr2

05-31-2009, 05:46 PM

This is what I have for y but I am having problems with finding x. I am not sure how to and need to show the work. I'm also not sure if the y is correct as well. I really appreciate any help someone can give me. Thanks :?

5x+11y=55

X=7-y

5x-11y=-55

X+y=7

5x-11y= -55

5(x+y)=5x7

5x=11y=-55

5x+5y=35

5x-11y= -55

-5x+5y= -35

6y= -20

Y=3.3

Mrspi

05-31-2009, 08:11 PM

This is what I have for y but I am having problems with finding x. I am not sure how to and need to show the work. I'm also not sure if the y is correct as well. I really appreciate any help someone can give me. Thanks :?

5x+11y=55

X=7-y

5x-11y=-55<-----where did THIS equation come from??

X+y=7

5x-11y= -55

5(x+y)=5x7

5x=11y=-55

5x+5y=35

5x-11y= -55

-5x+5y= -35

6y= -20

Y=3.3

You started with this:

5x + 11y = 55

x = 7 - y

SUBSTITUTE (7 - y) for x in the first equation:

5(7 - y) + 11y = 55

35 - 5y + 11y = 55

Now...take it from there. You seem to have done some arbitrary changing of signs (+ to - and vice versa)...you can't DO that!

Solve

35 - 5y + 11y = 55

for y.

Once you know the value of y, substitute it into

x = 7 - y

to find x.

Be sure to check that your values for x and y make BOTH of the original equations true.

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