algebra
posted by aneme .
how do you use the substitution method to solve the linear system?
2x5y=7
7x=y=8

Is 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. 
7x+y=8
i don't understand what you mean. could you possibly do an example? 
We 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.
2x5y = 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! 
whats the answer to 2x5y=7
7x+y=8