How do solve the following linear system?: # 3x + y =20 , -3x -8y = -9 #?

1 Answer
Mar 9, 2016

Answer:

#x=(151/21)# and #y=(-11/7)# or in other words the solution is the ordered pair #(151/21,-11/7)#

Explanation:

We will use the "Elimination Method" to help us start to solve this problem. I can easily eliminate the #x# variable by addind the two equations:
#3x+y =20#
#-3x-8y=-9# by adding like terms we get:

#-7y =11#
#y =-11/7#
Now that I have a value for #y#, I will substitute that in the first equation and solve for #x#
#3x+y=20#
#3x +(-11/7) = 20#
#3x = 20+11/7# I need a common denominator, which is #7#
#3x = 140/7 + 11/7#
#3x=151/7# Divide both sides of the equation by #3#
#x=151/21#