Which of the following would be the best first step when solving the following system using the substitution method?

Question

• x - y = -4 ;
• x + 2y = 5

x = -4 - y

x = -4 + y

2y = 5 - x

2y = 5 + x

I have solved the equation but I am unsure which is the best first step.

x-y=-4
x+2y=5
y=x+4

x+2y=5
x+2(x+4)=5
x=-1

y=x+4
y=-1+4
y=3

Could you please tell me which is the best first step?

Answer 1

If you insist on using substitution the logical first step is
x = -4 + y

then
-4 + y + 2 y = 5
3 y = 9
y = 3