How do solve the following linear system?: # x + y= 12 , 3x + y = -20 #?

2 Answers
Mar 23, 2016

line up the system of equations making sure that the variables are in the same relative positions.
#(x+y=12. eq.1)/(3x+y=-20 . eq.2)#

subtract equation 2 from equation 1
this will eliminate the y variable since they both have the same coefficient and same sign.

#-2x=32#

solve for x
x = -16

now substitute the value for x into either the first or second equation (doesn't matter). A good choice would be to pick the simplest equation of the two and this looks like equation 1.
By substituting x = -16 into eqn,1, you will now be able to solve for the y value.

Mar 23, 2016

Answer:

#x=-16#
#y=28#

Explanation:

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#x=-16#
#y=28#