How do you solve the following system?: 3x−6y=21,−x−3y=−7

1 Answer
Pallu
Oct 8, 2017

x=7 and y=0

Explanation:

3x−6y=21 -----------Let this be equation(1), and
−x−3y=−7 ---------- Let this be equation(2)

From (2), by transposition method, we have :

−x−3y=−7

−x=−7+3y

x=7−3y ---------------let this be equation (3).

Substitute vale of x from equation (3) in equation (1):

3x−6y=21

3(7−3y)−6y=21

21−9y−6y=21

21−15y=21

−15y=21−21

y=0−15

y=0

From (3) , we can get value of x:

x=7−3y

x=7−3(0)

x=7−0

x=7

therefore we have:

x=7 and y=0

Cross check by substituting values of xand y in equation (2):
−x−3y=−7
−7−3(0)=−7
−7−0=−7
−7=−7

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