Algebra 2 . Substitution. mutliple choice!

Question

anonymous · Answer

If you were to use the substitution method to solve the following system, choose the new equation after the expression equivalent to y from the first equation is substituted into the second equation. 

2x – y = –4 
5x – 6y = 12 

 5(–2x – 4) – 6y = 12 

 5(2x + 4) – 6y = 12 

 5x – 6(–2x – 4) = 12 

 5x – 6(2x + 4) = 12

anonymous · Answer

can you solve $2x-y=-4$ for $y$?

anonymous · Answer

would you subtract 2x from both sides

anonymous · Answer

yes you could do that
you would get 
$$-y=-2x-4$$ but you have one more step to get $y$

anonymous · Answer

i meant like. 
2x-y=-4
-2x     -2 
y=-2?

anonymous · Answer

no like this 
2x - y = -4 
-2x       -2x

-y = -2x - 4

anonymous · Answer

if you subtract $2x$ from both sides you get $-2x-4$ on the right

anonymous · Answer

oh okay. so whats next

anonymous · Answer

hope that is clear, you do not subtract 2x from the left and 2 from the right
next step is to solve for $y$ 
you have $-y=-2x-4$ and you want $y$ not $-y$ so multiply both sides by $-1$ which is the same as changing all the signs

anonymous · Answer

what do you get ?

anonymous · Answer

y=2x+4?

anonymous · Answer

exactly!

anonymous · Answer

now for the last step
replace $y$ in the equation $5x – 6y = 12 $ by $2x+4$ 
use parentheses

anonymous · Answer

is that step clear?  it should look exactly like on of your possible answers above

anonymous · Answer

5x-6(2x+4)=12?

anonymous · Answer

you got it

anonymous · Answer

thankyou very much :) so it's the last one?!

anonymous · Answer

yes it is the last one