How do we transform System A into System B?

System A
3x-5y=3
7x-8y=-15

System B
3x-5y=3
x+2y=-21

I just can't figure out what I multiple 7x-8y=-15 by to get x+2y=-21.

Question

How do we transform System A into System B?

System A
3x-5y=3
7x-8y=-15

System B
3x-5y=3
x+2y=-21

I just can't figure out what I multiple 7x-8y=-15 by to get x+2y=-21.

anonymous · Answer

@johnweldon1993

amoodarya · Answer

multiply first equation by -2 
then add by 2nd equation 
you will have the answer easy

amoodarya · Answer

3x-5y=3 
7x-8y=-15

multiply by -2 the 1st eq.
-6x+10y=-6 
so add by 7x-8y=-15

amoodarya · Answer

3x-5y=3
 7x-8y=-15

3x-5y=3 
(-6x+10y=-6 ) +(7x-8y=-15 )

anonymous · Answer

Oh, I was trying to do it completely wrong. Thank you!