Wednesday

November 26, 2014

November 26, 2014

Posted by **aneme** on Tuesday, February 12, 2008 at 9:42pm.

-2x-5y=7

7x=y=-8

- algebra -
**drwls**, Tuesday, February 12, 2008 at 10:12pmIs the second line supposed to be 7x + y = -8, or 7x - y = -8? You sweem to have inserted a second equal sign by mistake.

Whichever it is, use the second equation to derive an equation for y in terms of x. Then substitute that "y" value into the first equation, and it will be an equation in x only. Solve it.

- algebra -
**aneme**, Tuesday, February 12, 2008 at 10:21pm7x+y=-8

i dont understand what you mean. could you possibly do an example?

- algebra -
**Guido**, Wednesday, February 13, 2008 at 4:32pmWe have this:

How do you use the substitution method to solve the linear system?

-2x - 5y = 7...Equation A

7x - y = -8...Equation B

The idea is to isolate y OR x (your choice) and then plug that into EITHER Equation A or B (your choice).

I will isolate y in Equation B.

7x - y = -8...Equation B

-y = -7x - 8

y = (-7x - 8)/-1

y = 7x + 8

Do you see that we NOW know that y is 7x + 8?

To find x, I will plug 7x + 8 into EITHER Equation A or B.

I will choose Equation A.

-2x-5y = 7...Equation A

-2x - 5(2x + 8) = 7

-2x - 10x - 40 = 7

-12x - 40 = 7

-12x = 7 + 40

-12x = 47

x = 47/-12

x = -47/12...Value for x.

We just found the value of x and it is

-47/12. See it above?

We now plug our value for x into EITHER Equation A or B to find the value of y.

I will choose Equation A again.

-2x -5y = 7...Equation A

-2(-47/12) - 5y = 7

47/6 - 5y = 7

-5y = -47/6 + 7

-5y = -5/6

y = -5/6 divided by -5

y = 1/6

The solution for this system of linear equations in two variables is

x = -47/12 and y = 1/6.

We can also write the solution this way:

(-47/12, 1/6) = (x, y), where x represents -47/12 and y represents 1/6.

Done!

- algebra -
**Aaron R**, Thursday, February 21, 2008 at 7:02pmwhats the anserw to -2x-5y=7

7x+y=-8

- algebra -

**Answer this Question**

**Related Questions**

algebra - Requesting help. (I must reckon, that X is a variable, and y is y-...

maths - use the substitution method to solve the linear system. 1. 3x=9 -x+2y=9 ...

Algebra - Use the substitution method to solve the linear system. 1/8p+3/4q=7 3/...

algebra - Use the substitution method to solve the linear system. Thanks! s= t+4...

Algebra - -3x + 2y = 8 x + 4y = -4 use substitution method to solve the linear ...

algebra - use method of substitution to solve the system of linear equation 3x+...

algebra 1 - use the substitution method to solve the linear system. 9x+6y=3 3x-...

algebra - use method of substitution to solve the system of linear equations. 2x...

Algebra - Use substitution method to solve the linear system. Can someone please...

math - Use a substitution method to solve the linear system 2a=8 a+b=2