How do you solve the system of equations #2x=-y+6# and #-4x+3y=8#?

1 Answer
Jul 16, 2017

See a solution process below:

Explanation:

Step 1) Multiply each side of the first equation by #color(red)(-2)# so the #x# coefficient is #-4#:

#2x = -y + 6#

#color(red)(-2) xx 2x = color(red)(-2)(-y + 6)#

#-4x = (color(red)(-2) xx -y) + (color(red)(-2) xx 6)#

#-4x = 2y - 12#

Step 2) Solve the second equation for #-4x#:

#-4x + 3y = 8#

#-4x + 3y - color(red)(3y) = 8 - color(red)(3y)#

#-4x + 0 = 8 - 3y#

#-4x = 8 - 3y#

Step 3) Because both equations are now solved in terms of #-4x# we can equate the right side of each equation to each other and solve for #y#:

#2y - 12 = 8 - 3y#

#2y - 12 + color(red)(12) + color(blue)(3y) = 8 - 3y + color(red)(12) + color(blue)(3y)#

#2y + color(blue)(3y) - 12 + color(red)(12) = 8 + color(red)(12) - 3y + color(blue)(3y)#

#(2 + color(blue)(3))y - 0 = 20 - 0#

#5y = 20#

#(5y)/color(red)(5) = 20/color(red)(5)#

#(color(red)(cancel(color(black)(5)))y)/cancel(color(red)(5)) = 4#

#y = 4#

Step 4) Substitute #4# for #y# in the solution to either equation at the end of Step 1 or Step 2 and solve for #x#. Either equation can be used. I will use the equation from Step 1:

#-4x = 2y - 12# becomes:

#-4x = (2 * 4) - 12#

#-4x = 8 - 12#

#-4x = -4#

#(-4x)/color(red)(-4) = -4/color(red)(-4)#

#(color(red)(cancel(color(black)(-4)))x)/cancel(color(red)(-4)) = 1#

#x = 1#

The Solution Is: #x = 1# and #y = 4# or #(1, 4)#