How do you solve #2x+y= -1 # and #-x+y= -7# using substitution?

1 Answer
Jul 2, 2018

Answer:

#color(magenta)(x = 2, y = -5#

Explanation:

#2x + y = -1 " Eqn (1)"#

#-x + y = -7#

#x - y = 7 " Eqn (2)"#

#color(crimson)("1. Using elimination process"#

Adding Eqns (1) & (2),

#2x + x +cancel( y - y) = -1 + 7#

#3x = 6 " or " x = 2#

Substituting value of 'x' in Eqn (1),

#2*2 + y = -1#

#y = -1 + -4 = -5#

#color(crimson)("2. Using substitution process"#

#x = y + 7 " from Eqn (2)"#

Substituting value of 'x' in Eqn (1)",

#2 * (y + 7) + y = -1#

#3y = -1 -14 = -15#

#y = -5#

Substituting value of 'y ' in Eqn (2),

#x - (-5) = 7#

#x = 7 - 5 = 2#