Question 1113803

Can this system by solved by substitution?
6x + 7y = -9
-4x - 5y = 5
<pre>You don't have to deal with ANNOYING fractions by solving for a variable right away. IGNORE anyone who tells you to do that.
In this particular case, ADD the 2 equations to get eq (iii) in the form of: 2x + 2y = - 4
Reduce eq (iii) by dividing it by 2 to get: x + y = - 2____x = - 2 - y
Now, substitute this value for x in any of the 2 equations. I chose eq (ii), and got: - 4(- 2 - y) - 5y = 5
8 + 4y - 5y = 5
4y - 5y = 5 - 8
- y = - 3
{{{highlight_green(matrix(1,5, y, "=", (- 3)/(- 1), "=", 3))}}} 
You then substitute 3 for y in any of the original equations to get x. I chose eq (ii), and got: - 4x - 5(3) = 5
- 4x - 15 = 5
- 4x = 20
{{{highlight_green(matrix(1,5, x, "=", 20/(- 4), "=", - 5))}}}