Use elimination or substitution to solve

Question

Y+3x=-21

X-3=3y

Answer 1

Dear Larenzo,

    If you want to use elimination, then X-3=3Y would have to be in standard linear form (AX+BY=C, where C is your constant number.  Let's try substitution:    Solve for X in the second equation:   X-3=3y.

 

X-3=3Y            Add +3 to both sides

 

 

X=3Y+3           Then substitute this value for X into the top equation:

 

 

Y+ 3X= -21                 Y+3(3Y+3)= -21        Use the distributive property to simplify the middle term.

 

 

1Y+ 9Y+9=-21              Collect like terms.

 

 

10Y + 9 = -21     Add a -9 , or subtract 9 from both sides.  Both procedures get you the same result.

 

 

10Y= -30                  Divide both sides by the number next to "Y."

 

 

Y=-3                         Substitute this value into the second equation to find the "X" value because the second

 

equation is easier.   I am going to allow you to finish this problem.  If there are further questions, just let me know.

 

If I have helped you, please give me a thumbs up.

 

                                                              Susan C.

 

 

Answer 2

x=3y+3

y+3(3y+3)=-21

y+9y+9=-21

10y=-30

y=-3

x=3*(-3) +3 = -6

so x=-6, y=-3