could someone help me with me substitution method?

Question

x-y=3

x=2y+9 

 

 

Answer 1

I would plug the second equation into the first and then solve for the value of y!

(2y + 9) - y = 3

y + 9 = 3

y = -6

then you can circle back to the second equation to find

x = 2(-6) + 9

x = -12 + 9

x = -3

Answer 2

x-y=3
x=2y+9

 

Okay, I'll do it for you, if you promise to learn from this.

 

Since x equals 2y+9, I will replace (substitute) x by 2y+9 in the FIRST EQUATION;

I  get:   2y+9 - y = 3

Then I 'collect or combine' like terms; now I have  y + 9 = 3

 

Next, after I subtract 9 from each side I have  y  =3-9, that is, y = -6.

 

Finally, I use this value of y in the second equation (substituting it in place of "y"); I get x = 2(-6) + 9;

so x = -12 + 9;  x = -3.

 

The solution is the ordered pair (-3, -6).  Check these two equations substituting these two values; in each case the left side number should equal the right side number.  In a graphing sense, we've just found the point of intersection of two lines.