Step 1) Solve the first equation for #x#:
#-4x + 4y = 4#
#-4x + 4y - color(red)(4y) = 4 - color(red)(4y)#
#-4x + 0 = 4 - 4y#
#-4x = 4 - 4y#
#(-4x)/color(red)(-4) = (4 - 4y)/color(red)(-4)#
#x = 4/color(red)(-4) - (4y)/color(red)(-4)#
#x = -1 + y#
Step 2) Substitute #(-1 + y)# for #x# in the second equation and solve for #y#:
#y = 9x + 73# becomes:
#y = 9(-1 + y) + 73#
#y = (9 * -1) + (9 * y) + 73#
#y = -9 + 9y + 73#
#y - color(red)(9y) = -9 + 9y - color(red)(9y) + 73#
#1y - color(red)(9y) = -9 + 0 + 73#
#(1 - color(red)(9))y = -9 + 73#
#-8y = 64#
#(-8y)/color(red)(-8) = 64/color(red)(-8)#
#y = -8#
Step 3) Substitute #-8# for #y# in the solution to the first equation at the end of Step 1 and calculate #x#:
#x = -1 + y# becomes:
#x = -1 + (-8)#
#x = -1 - 8#
#x = -9#
The Solution Is:
#x = -9# and #y = -8#
Or
#(-9, -8)#
