solve system of equations by substitution x+y=9 y=2x

x + y = 9

y = 2x

Place the 2nd equation into the first in place of y

x + (2x) = 9

Simplify

3x = 9

Divide on both sides

x = 3

Now we have to find y, so plug x into the 2nd equation

y = 2(3)

Multiply

y = 6

Now put x and y into point form (x,y)

(3,6)

x+y=9 y=2x

Subbing the second equation into the first for y, we have

x + (2x)  = 9    simplify

3x = 9             divide by 3 on both sides

x = 3

And y = 2x  = 2(3)  = 6

So....our solution is

(3, 6)

I'll give you all the points here, saseflower, since my answer basically echoed yours.....good job....

Oh okay! Thanks, CPhill