Using the substitution method, I'm asked to solve this system of equations. x=5y+7, 15y=-3x+21. So I would take 5y+7 and substitute for x in 15y= -3(5y +7)+21, which gives me 15y=-15y-21+21 and then I am left with 15y=-15y. Now what do I do? I'm stuck.

Question

Using the substitution method, I'm asked to solve this system of equations.  x=5y+7, 15y=-3x+21.  So I would take 5y+7 and substitute for x in 15y= -3(5y +7)+21,  which gives me 15y=-15y-21+21 and then I am left with 15y=-15y.  Now what do I do?  I'm stuck.

miracrown · Answer

that gives you y=0

phi · Answer

you could add +15y to both sides

llroberts43 · Answer

ok, I'm overthinking it again.  I see now.  Thank you

miracrown · Answer

15y = -15y

=> 15y  + 15y = 0

now, solve for x