How do you solve the simultaneous equations #4x + y = 9 # and #2x - y = 3#?

1 Answer
Jul 13, 2015

Answer:

Since both given equations contain similar coefficients for #y#, the simplest method is to add the two equations and solving single variable equations to get
#(x,y) =(2,1)#

Explanation:

[1]#color(white)("XXXX")##4x+y = 9#
[2]#color(white)("XXXX")##2x-y = 3#

Add [1] to [2] giving
[3]#color(white)("XXXX")##6x = 12#
Divide both sides by #6#
[4]#color(white)("XXXX")##x = 2#
Using information from [4], replace #x# with #2# in [1]
[5]#color(white)("XXXX")##4(2)+y = 9#
Simplify
[6]#color(white)("XXXX")##y=1#