How do you solve the following system?: #-21x+3y=21 , -6x+3y=17 #

1 Answer
Nov 29, 2015

Answer:

#(-4/15 , 77/15)#

Explanation:

Given system of equation
#-21x+3y= 21 " " " " " " (1) #
#-6x+3y =17 " " " " " " (2)#

Multiply the first equation by #-1#

#-1 * (-21x+3y=21)#

#21x-3y=-21 " " " (3)#

Add equation #(2)# from equation #(3)#

#21x-3y=-21#
#-6x+3y=17#
#stackrel("--------------------------------")#

#15x = -4#

#color(red)(x =- 4/15)#

Substitute #x=-4/15# for #y# in equation #(1)#

#-21*(-4/15) + 3y= 21#

#28/5 +3y =21#

#5(28/5+3y=21)#

#28+15y =105#

#15y= 77#

#color(red)(y = 77/15)#